JPH0314868Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention relates to a reception mode discrimination circuit for a television audio multiplex broadcast receiver.

(b) Prior Art Recently, television audio multiplex broadcasting has started in the United States, but this system is significantly different from the Japanese system, as shown in Figure 2, which shows the frequency spectrum of the multiplexed signal. There is. That is, this second
In the system shown in the figure, secondary audio such as foreign language broadcasting, or SAP
(separate andio program) channel is provided independently from the channel for the stereo difference signal (L-R), and moreover, it is important that the L-R channel signal and the SAP channel signal can be transmitted simultaneously. It is a characteristic.

Therefore, in a receiver for such an audio multiplexed signal, it is necessary to accurately determine the stereo reception mode and the SAP reception mode, and set the receiver to each mode. For this reason, the present applicant previously proposed Utility Model Application No. 59-38345 (U.S. Pat. No. 150861)
There is something that was proposed. That is, this method:
Detection output of subcarrier of SAP channel signal and L
- The level of the detection output of the high frequency component above the R channel signal band is compared, and the SAP reception mode is determined only when the two have a predetermined level relationship.

By using such a method, the SAP reception mode can be determined reliably, but on the other hand, the stereo reception mode is generally detected using the method shown in FIG. 2, which is performed only by detecting the stereo pilot signal. Therefore, there was a risk that the pilot signal detection circuit would malfunction due to noise, and would be determined to be in stereo reception mode even when stereo reception was not being performed.

(c) Problems to be solved by the invention The present invention enables the above-mentioned audio multiplex broadcasting receiver to suitably discriminate between the sub-audio reception mode and the stereo reception mode, and also makes the discrimination circuit as simple as possible. The challenge is to configure it.

(d) Means for solving the problem In order to solve the above problem, the present invention includes a first discrimination circuit that obtains the detection output of the stereo pilot signal and discriminates the stereo reception mode;
Get the subcarrier detection output of SAP channel signal
In addition to the second discrimination circuit that discriminates the SAP reception mode, a detection circuit that detects noise components in the sub-audio channel band or above is provided, and the operation of the first and second discrimination circuits is controlled by the output of this detection circuit. I try to control each.

(E) Effect In the above configuration, when a detection output of a predetermined level or higher is generated due to noise in the multiplexed signal, the detection circuit forces each of the first and second discrimination circuits to perform non-stereo reception. mode and non-SAP reception mode, thereby preventing the first and second discrimination circuits from malfunctioning due to noise or the like.

(f) Embodiment In an embodiment of the present invention shown in FIG. 1, reference numeral 1 is an input terminal for receiving and demodulating the television audio multiplexed signal shown in FIG. 2 is a first discrimination circuit that discriminates the stereo reception mode, and basically converts the stereo pilot signal in the multiplexed signal into a PLL.
It consists of a pilot signal detection circuit 3 that detects a signal using a (phase-locked loop) circuit, and a switching circuit 4 that includes transistors Q ₁ to _{Q 5} that operate in response to the detection output of the pilot signal detection circuit 3 and the output of a noise detection circuit that will be described later. ing.

Next, 5 is a second discrimination circuit that discriminates the SAP reception mode, and includes a bandpass filter 6 for extracting the SAP channel signal, and transistors Q ₆ and Q ₇ .
narrowband tuned amplifier 7 with diode D ₁ ,
The SAP subcarrier detection circuit 9 includes a smoothing circuit 8 including D ₂ and a capacitor C ₂ , and a level comparator 10 whose detection output is input to a non-inverting input terminal. And the tuning amplifier 7
is tuned to subcarrier 5H of the SAP channel by coil L and capacitor _C1 [see Figure 3 A]
I'm starting to do that.

Further, 11 is a noise detection circuit that detects high-frequency noise components above the SAP channel band in the multiplexed signal, and this circuit includes transistors Q ₈ ,
A non-tuned broadband amplifier 12 (see Figure 3 B) consisting of Q ₉ and capacitors C ₃ and C ₄ , etc., and a diode.
Smoothing circuit 13 with D ₃ , D ₄ and capacitor C ₅ etc.
The output of this noise detection circuit 11 is input to the inverting input terminal of the comparator 10, and is also input to the fifth transistor _Q5 of the switching circuit 4 via the resistor _R1 and the Zener diode ZD.
is applied to the base of the In addition,
A constant positive voltage is applied to the anode side of the diode D ₃ in the smoothing circuit 13 by resistors R ₂ , R ₃ and capacitor C ₇ .

Now, in this embodiment, a high gain tuned amplifier 7 is used in the SAP subcarrier detection circuit 9,
and a diode in the noise detection circuit 11.
Since an appropriate bias voltage is applied to D ₃ as described above, if there is an SAP channel signal in the received multiplexed signal, and it is in a medium to strong electric field reception state and there is little noise, the fourth As shown by the solid line in the figure, the SAP detection output voltage a obtained at point A is always higher than the noise detection output voltage b obtained from the noise detection circuit 11 at point B. Therefore, at this time, the output of the comparator 10, that is, the output voltage of the second output terminal 15 becomes "high", indicating that the SAP channel signal is being received (ie, SAP reception mode).

On the other hand, when there is no SAP channel signal in the multiplexed signal, as long as large noise does not appear within the SAP channel signal band, the signal will remain as shown by the broken line in Figure 4, regardless of changes in the received electric field strength.
The SAP detection output voltage a is lower than the noise detection output voltage b. Furthermore, even if an SAP channel signal exists in the multiplexed signal, when there is a weak electric field reception state and there is a lot of noise, the relationship between the detected output voltages a and b is reversed as shown at the left end of the solid line in Figure 4. . Therefore, in each of these cases, the output voltage of the second output terminal 15 becomes "low" and becomes non-active.
Indicates SAP reception mode.

In addition, in FIG. 4, the noise detection output voltage b changes between the presence (solid line) and absence (dashed line) of the SAP channel signal because the SAP subcarrier also changes in the broadband amplifier 12. This is because the signal is slightly amplified and output (see FIG. 3B). Also,
The telemetry channel signal with 6.5H as a subcarrier in the multiplexed signal in FIG. 1 is also input to the amplifier 12 and output to the noise detection circuit 11 .
Since this signal is selected to have a lower level than the SAP channel signal, the detection output will not cause any malfunction in the determination operation.

Next, if a stereo pilot signal is present in the multiplexed signal, a "high" voltage is applied from the pilot signal detection circuit 2 to the base (point C) of the first transistor _Q1 of the switching circuit 4. Ru. On the other hand, the output voltage b of the noise detection circuit 11 is connected to a Zener diode ZD via a resistor _R1.
However, in the above-mentioned medium to strong electric field reception state, the noise detection output voltage b is applied to the Zener diode ZD.
Since the current level is below the conduction start level (C in FIG. 4), this diode does not conduct and the fifth transistor _Q5 also turns off. As a result, the fourth transistor _Q4 is turned on and a voltage lower than the detected output voltage at point C appears at point D, so the first transistor _Q1 is turned on and the second transistor _Q2 is held off. A "high" output voltage is derived from the collector of the second transistor _Q2 , that is, the first output terminal 14, indicating the stereo reception mode.

On the other hand, if the stereo pilot signal does not exist in the multiplexed signal, the detected output voltage at point C is approximately 0V.
When the voltage reaches , the fourth transistor _Q4 turns on,
Regardless of whether it is off or not, it will be lower than the voltage at point D, so
Regardless of the received field strength, the first transistor Q ₁
is off and the second transistor _Q2 is on. Furthermore, even if the pilot signal detection circuit 3 malfunctions due to noise in a weak electric field reception state and its output voltage appears at point C, the noise detection voltage b at point B will be the fourth As the height increases as shown at the left end of the diagram, the Zener diode ZD conducts and the fifth transistor _Q5 turns on, which turns off the fourth transistor _Q4 , so the point D is much higher than the point C. Once again, the first transistor Q ₁ is off and the second transistor Q ₂ is on. Therefore, in both of these two cases, the first
A "low" voltage appears at the output terminal 14, indicating a non-stereo reception mode.

Note that each discrimination output obtained at the first and second output terminals 14 and 15 is introduced into a reception mode selection circuit (not shown), so that the reception mode can be selected according to the viewer's wishes. Since this is not directly related to the gist of the present invention, further explanation will be omitted.

In addition, in the above embodiment, the pilot signal detection circuit 3 and the switching circuit 4 are constructed of discrete circuits, but an FM multiplex stereo demodulation circuit including circuits equivalent to both of the above circuits in one chip may be used.
Even if an IC is used, it can be realized in the same manner as in the above embodiment. That is, as the above IC, for example, Tokyo Sanyo Electric Co., Ltd.
When using the LA3350A from Manufacturer, when a high level positive voltage is applied to the pin of this IC,
Since the detection operation of the stereo pilot signal in the multiplexed signal input to the pin is stopped and the non-stereo reception mode is forced, the noise detection output voltage b obtained at point B in Figure 1 at the above pin is The configuration may be such that the voltage is applied via a diode or the like.

(g) Effects of the invention According to the receiving mode discrimination circuit of the present invention, discrimination of sub-audio reception mode and stereo reception mode can be reliably performed in appropriate reception conditions such as when receiving a medium to strong electric field. This makes it possible to prevent malfunctions in the above-mentioned discrimination operations or meaningless discriminations due to noise in the multiplexed signal when the reception condition is poor, such as in the case of a weak electric field. Moreover, since the noise detection circuit is also used as the first and second discrimination circuits for discriminating each mode, the circuit configuration is extremely simple.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure shows the frequency spectrum of the American television audio multiplex signal, Figure 3 A and B show the characteristics of the two amplifiers in the above embodiment, and Figure 4
The figure is a characteristic diagram for explaining the operation of the above embodiment. 2: first discrimination circuit; 5: second discrimination circuit; 11:
Noise detection circuit.

Claims (1)

[Claims for Utility Model Registration] (1) A main channel signal consisting of a main audio or stereo sum signal, a stereo difference channel signal based on a first subcarrier, and a second subcarrier having a higher frequency than the first subcarrier. In a receiver that receives a television audio multiplex signal including a sub audio channel signal by a carrier wave and a stereo pilot signal inserted between the main channel signal band and the stereo difference channel signal band, the stereo pilot signal a first discrimination circuit that obtains the detection output of the second subcarrier and discriminates the stereo reception mode; a second discrimination circuit that obtains the detection output of the second subcarrier and discriminates the subaudio reception mode;
a detection circuit that detects noise components in the sub-audio channel band or higher in the multiplexed signal,
A receiving mode discriminating circuit for a television audio multiplex broadcast receiver, wherein each discriminating operation of the first and second discriminating circuits is controlled according to the output of the detecting circuit. (2) The second discrimination circuit includes a level comparison circuit which takes the detection output of the second subcarrier as one input and the output of the detection circuit as another input, and the first discrimination circuit is provided with the output of the detection circuit. 2. The receiving mode discriminating circuit according to claim 1, further comprising a switching circuit that disables the detection output of the stereo pilot signal when the stereo pilot signal is detected.