JPS6111511B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a television audio receiver, and an object of the present invention is to provide a circuit that can correctly receive only audio signals without being interfered with by video signals.

There are television audio receivers that receive only the audio signals of television broadcasts and listen to them with better sound quality. Such receivers are also used to receive audio multiplex broadcasts. Normal television receivers use a circuit called an intercarrier system that amplifies both video and audio signals at the same time, but this system requires a means to prevent buzz from coming out of the speakers. It is difficult to obtain good sound quality. In particular, when receiving an audio multiplex broadcast, the buzz sound becomes a source of interfering sound called a buzz beat, further degrading the sound quality. On the other hand, since television audio receivers only need to be able to receive audio signals, it is advantageous to adopt the so-called separate carrier system (split carrier system), which is superior to the intercarrier system in terms of sound quality. With this separate carrier method, only the audio signal is received and amplified independently, so the audio is not interfered with by the video signal or synchronization signal, and there is no buzz and excellent linearity can be obtained.
It is something that When a receiver using such a separate carrier system uses a dial type tuning means in which the tuning frequency changes continuously, it is difficult to correctly receive an audio signal band narrower than the video signal band. . Furthermore, since the device is tuned not only to the audio signal but also to the video signal, there may be cases where no sound is produced or a buzzing sound is generated even though the device is in the tuning state. In such a case, since the device is tuned to the video signal, the operator must turn the tuning knob again, which is confusing for the operator and is not easy to operate.

The present invention improves these drawbacks, and one embodiment of the present invention will be described below with reference to the drawings.

In Fig. 1, 1 is an antenna, 2 is a tuner,
3 is a mixing circuit, 4 is a local oscillator, 5 is an IF amplifier, 6 is a limiter, 7 is an FM detection circuit, 8 is a de-emphasis circuit, 9 is a mutating circuit, 10 is a low frequency amplifier, and low frequency amplifier 1
The zero output is applied to the speaker via terminal 11. 12 is a muting signal generation circuit;
It consists of a video detection circuit 13, a level detection circuit 14, a tuning detection circuit 15, and an OR circuit 16.

In this configuration, when tuned to a video signal, an output is output from the video detection circuit 13, and this output detects that it is not an audio signal, and the tuning display circuit 17 connected to the OR circuit 16 is not operated, and further tuning is performed. The tuning display circuit 17 is not turned on until the knob is turned to tune the audio signal.

The image detection circuit 13 is shown in FIG. 2, and the output of the IF amplifier 5 shown in FIG. , and only a synchronizing signal is obtained from the transistor 20 as shown in FIG. 6E. This waveform E
is peak-detected by the diode 21 and the capacitor 22, and becomes a DC signal shown in FIG. 6F, which is applied to the OR circuit 16. In other words, the DC signal is applied to the OR circuit 16 only when it is tuned to the video signal.

What is shown in FIG. 3 is the level detection circuit 14,
The output of the limiter 6 is applied, and the transistor 23
Since a signal with the characteristics shown in Figure 6A is obtained on the base side of the circuit, a certain threshold level is set so that the output changes as shown in Figure 6B when the signal is above and below a certain level. Determine transistor 23 and its bias. This transistor 2
3 is applied to the OR circuit 16.

What is shown in FIG. 4 is the tuning detection circuit 15,
The S-shaped output of the FM detection circuit 7 (Fig. 6G) is applied to transistors 24 and 25 that constitute a differential amplifier.
As shown in FIG. 6H, an output is obtained which changes depending on whether it is in tune, out of tune, or out of tune, and this output is applied to the OR circuit 16.

The OR circuit 16, as shown in FIG.
The output obtained by inverting the input of this Schmitt trigger circuit lights up the light emitting diode 27, which is the display element 27, to indicate that it is tuned to the audio signal.
Note that the light emitting diode 27 may be a display element such as a meter. Furthermore, OR circuit 16
By activating the muting circuit 9 with the output of , the sound is produced only at the correct audio tuning point, and when the video signal is synchronized or out of synchronization, the muting circuit is activated to prevent noise from being generated.

In Figure 1, the audio IF frequency of mixed circuit 3 is 54.25MHz in a general TV tuner, but it is further mixed with local oscillation output and set to 10.7MHz, which is equal to the IF of a normal stereo broadcast receiver, making signal processing easier. I can think of something to do. This method is called the double superheterodyne method, and it mixes the 64.95MHz local oscillation output with the IF signal (54.25MHz) to obtain an IF of 10.7MHz. At this time too,
It goes without saying that the correct synchronization of the audio can be determined using a method similar to that described above. However, in this case, when detuned by Δ, the audio IF (54.25M
Hz), the video IF (58.75MHz), and the local oscillator's 64.95MHz.The sum of the mixed components may be 10.7MHz. In other words, as is clear from the following equation, 10.7MHz
occurs.

64.95−(54.25+Δ) +)64.95−(58.75+Δ) 129.9−(113.0+2Δ) =16.9−2Δ=10.7 ∴Δ=3.1MHz At this tuning point, video components are also included and the buzz sound is
Since this occurs, it is necessary to apply muting, but as in the circuit described above, muting is applied when a video signal is present, and no problem will occur even if it is a double superheterodyne system.

In this way, the tuning display operates only when there is no video signal, the output level of the limiter is high, and the tuning is approximately at the center of the S-shaped characteristic output, making it easy to know when the device is correctly tuned to only the audio signal. It is something.

As described above, according to the present invention, in a separate carrier type television audio receiver, it is possible to prevent noise from being generated due to muting when the receiver is tuned to a video signal or other erroneous signal. Further, since the tuning display is not operated and the tuning display is performed only when the device is tuned to the audio signal, the tuning operation becomes extremely easy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a television audio receiver according to an embodiment of the present invention, and FIGS. 2, 3, 4, and 5 are circuit diagrams of the main parts of the receiver, respectively.
6A, B, C, C, E, F, G, and H are operational waveform diagrams of the same receiver. 5...IF amplifier, 6...Limitsuta, 7...FM
Detection circuit, 9... Muting circuit, 12...
Muting signal generation circuit, 13... Video detection circuit, 14... Level detection circuit, 15... Tuning detection circuit, 16... OR circuit, 17... Tuning display circuit. 〓〓〓〓

Claims (1)

[Scope of Claims] 1. A tuner capable of receiving audio signals of television broadcasting, means for converting the output of the tuner into an intermediate frequency signal, and a means for converting the intermediate frequency signal into at least an FM signal.
means for processing and reproducing audio by a detection circuit, a muting circuit, and a low frequency amplification circuit; and a means for detecting a video signal from the intermediate frequency signal;
A television audio receiver comprising means for operating the muting circuit based on the detection output when the video signal is detected. 2. A tuner capable of receiving television broadcast audio signals, means for converting the tuner output into an intermediate frequency signal, and processing of the intermediate frequency signal by at least a limiter, an FM detection circuit, a muting circuit, and a low frequency amplification circuit. means for detecting a video signal from the intermediate frequency signal and generating a detection output when the video signal is present; and means for generating the muting circuit using the detection output when the video signal is detected. means for activating the limiter; means for generating a detection output when the magnitude of the output signal of the limiter is below a certain level; and a means for generating a detection output when the output signal of the FM detection circuit is not in a state of tuning within a certain range. A television audio receiver comprising means for generating an out-of-synchronization detection output, and means for ORing these three detection outputs and operating a synchronization display only when synchronized to an audio signal. .