JPH06292102A - Television receiver - Google Patents

Abstract

PURPOSE:To attain AM detection in a demodulation circuit for FM detection by multiplying a sound component obtained from an intermediate frequency signal of a television signal with a fundamental signal obtained by limiting the amplitude of the sound component at the same phase and demodulating the result. CONSTITUTION:A tuner 2 selects a designated channel and converts a television signal into an intermediate frequency signal to provide an output to a preamplifier and a SAW filter 3. An SIF filter 8 extracts an AM-modulated sound component from a video/sound intermediate frequency signal subject to AM detection to provide an output to a limiter 11 and to a demodulation circuit 14 comprising a multiplier circuit. The limiter 11 limits the amplitude of the sound component received from the SIF filter 8 to provide the result as an output to the demodulation circuit 14 as a fundamental signal. Then the demodulation circuit 14 multiplies the fundamental signal inputted from the limiter 11 with the sound component inputted from the SIF filter 8 for the same phase to apply AM detection and to extract a sound signal and it is outputted to a 3rd output terminal 15 of an IF use IC (intermediate frequency integrated circuit) 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver for demodulating an AM-modulated audio signal.

[0002]

2. Description of the Related Art FIG. 3 is an explanatory diagram showing the structure of a conventional television receiver. That is, the television signal composed of the FM-modulated audio signal and the AM-modulated video signal is received by the receiving antenna 1
Is received by and input to the tuner 2. The tuner 2 selects a designated channel, converts it into an intermediate frequency signal, and outputs it to the pre-stage amplifier and the SAW filter 3. The pre-stage amplifier and SAW filter 3 amplifies the intermediate frequency signal input from the tuner 2 and extracts the video / audio intermediate frequency signal to extract the first intermediate frequency integrated circuit (IF IC) 4 from the first stage.
Is output to the AM detection circuit 6 via the input terminal 5. The AM detection circuit 6 AM-detects the video / audio intermediate frequency signal input from the pre-stage amplifier and the SAW filter 3 and I
It is output to the SIF filter 8 and the voice trap 9 via the first output terminal 7 of the F IC 4. This audio trap 9 is an AM-detected image input from the AM detection circuit 6.
An audio intermediate frequency signal of the audio intermediate frequency signal is excluded and a video signal is output. The SIF filter 8 is an AM detection circuit 6
The SIF signal is extracted from the AM-detected video / audio intermediate frequency signal input from the and is output to the limiter 11 via the second input terminal 10 of the IF IC 4. This limiter 1
Reference numeral 1 is for limiting the amplitude of the SIF signal input from the SIF filter 8 to remove the change in amplitude to form an FM wave of constant amplitude, which prevents the change in amplitude from appearing in the detection output and damaging the sound quality as noise. ing. The output signal from the limiter 11 is output to the discriminator 13 via the second output terminal 12 of the IF IC 4 and also to the demodulation circuit 14 including a multiplication circuit. The discriminator 13 advances the phase of the output signal from the limiter 11 by 90 degrees and outputs it to the demodulation circuit 14 via the third input terminal 16 of the IF IC 4. The demodulation circuit 14 multiplies the signal input from the limiter 11 and the signal input from the discriminator 13 with a 90-degree phase advance, performs FM detection, extracts a voice signal, and outputs the third output of the IF IC 4 It is output via the terminal 15.

In FIG. 5B, S1 is an output signal from the limiter 11, S2 is a signal output from the discriminator 13 with a 90-degree phase advance, and S3 is signals S1 and S2.
Is the output signal of the demodulation circuit 14, and the ground level (0 level) is that signals S1 and S2 are GND1 and signal S3 is GND2. Output signal S of the demodulation circuit 14
An audio signal is obtained by integrating 3.

Incidentally, S1 in FIG. 5C is the limiter 1 described above.
1 is an output signal, S2 is a signal output from the discriminator 13 with a phase advance of 180 degrees, and S3 is a signal S
The output signal of the demodulation circuit 14 obtained by multiplying 1 and S2,
Ground level (0 level) signals S1 and S2 are GND
1, the signal S3 is GND2.

FIG. 4 is a schematic structural explanatory view showing a television receiver (SECAM-L) for demodulating a conventional AM-modulated audio signal and video signal. That is, a television signal including an AM-modulated audio signal and video signal is received by the receiving antenna 2
It is received at 1 and input to the tuner 22. The tuner 22 selects a designated channel, converts it into an intermediate frequency signal, and outputs it to the preamplifier and the SAW filters 23 and 24, respectively. One of the pre-stage amplifiers and the SAW filter 23 amplifies the intermediate frequency signal input from the tuner 22, extracts the video intermediate frequency signal, and outputs it to the intermediate frequency integrated circuit (IF IC) 25. The IF IC 25 AM-detects the video intermediate frequency signal input from the pre-stage amplifier and the SAW filter 23 and demodulates and outputs the video signal. The other pre-stage amplifier and SAW filter 24 amplifies the intermediate frequency signal input from the tuner 22, extracts the audio intermediate frequency signal, and outputs it to the intermediate frequency integrated circuit (IF IC) 26. The IF IC 26 AM-detects the audio intermediate frequency signal input from the pre-stage amplifier and the SAW filter 24 and demodulates and outputs the audio signal.

[0006]

Therefore, in the conventional detection of the audio signal and the video signal (SECAM-L) which are AM-modulated, two pre-stage amplifiers and SAW filters and an IF are used.
It was uneconomical because two ICs were needed.

The present invention has been made in view of the above circumstances, and AM detection can be performed by using a demodulation circuit including a multiplication circuit for FM detection, the number of parts can be reduced, and the same demodulation can be performed. FM detection and AM using a circuit
An object of the present invention is to provide a television receiver capable of switching detection.

[0008]

In order to solve the above problems, a television receiver of the present invention is a frequency conversion means for receiving a television signal composed of an AM-modulated audio signal and a video signal and converting it into an intermediate frequency signal. A voice component extracting means for extracting a voice component from the intermediate frequency signal converted by the frequency converting means; an amplitude limiting means for limiting the amplitude of the voice component extracted by the voice component extracting means; and an amplitude limiting means. And a demodulation means for multiplying the output signal from the audio component and the audio component extracted from the audio component extraction means.

Further, the television receiver of the present invention receives a television signal composed of an AM-modulated audio signal and a video signal and converts it into an intermediate frequency signal, and an intermediate frequency converted by this frequency converting means. A voice component extracting means for extracting a voice component from the frequency signal, an amplitude limiting means for limiting the amplitude of the voice component extracted by the voice component extracting means, and a phase shift for shifting the phase of the output signal from the amplitude limiting means. Means, selecting means for selecting either the output signal from the phase shifting means or the voice component extracted from the voice component extracting means, the signal selected by the selecting means and the amplitude limiting means. And a demodulation means for multiplying the output signal.

[0010]

According to the present invention, by the above means, the audio component obtained from the intermediate frequency signal of the television signal composed of the AM-modulated audio signal and video signal and the basic signal whose amplitude is limited are multiplied in phase. Since it is then demodulated, AM detection can be performed using a demodulation circuit including a multiplication circuit for FM detection, the number of components can be reduced, and FM detection and AM detection can be switched using the same demodulation circuit. Can be possible.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a structural explanatory view showing an embodiment of the present invention. That is, a television signal including an AM-modulated audio signal and video signal is received by the receiving antenna 1 and input to the tuner 2. This tuner 2 selects a designated channel, converts it into an intermediate frequency signal, and converts it into a pre-stage amplifier and a SAW.
Output to filter 3. The pre-amplifier and SAW filter 3 amplifies the intermediate frequency signal input from the tuner 2 and extracts the video / audio intermediate frequency signal to connect the first input terminal 5 of the intermediate frequency integrated circuit (IF IC) 4 to it. It is output to the AM detection circuit 6 via the. The AM detection circuit 6 receives the image input from the preamplifier and the SAW filter 3.
The audio intermediate frequency signal is AM detected and output to the SIF filter 8 and the audio trap 9 via the first output terminal 7 of the IF IC 4. This voice trap 9 is an AM detection circuit 6
The audio intermediate frequency signal of the AM-detected video / audio intermediate frequency signal input from is removed and the video signal is output. The SIF filter 8 receives the AM input from the AM detection circuit 6.
An AM-modulated audio component is extracted from the detected video / audio intermediate frequency signal and output to the limiter 11 via the second input terminal 10 of the IF IC 4 and also via the third input terminal 16 of the IF IC 4. And is output to the demodulation circuit 14 including a multiplication circuit. The limiter 11 limits the amplitude of the audio component input from the SIF filter 8 and outputs it as a basic signal to the demodulation circuit 44. The demodulation circuit 14 receives the basic signal input from the limiter 11 and the SIF filter 8
AM by multiplying the voice components input from
The detection is performed and the audio signal is extracted and output via the third output terminal 15 of the IF IC 4.

5A, S11 is a basic signal from the limiter 11, S12 is a voice component having the same phase as the basic signal S11 output from the SIF filter 8, and S13.
Is the output signal of the demodulation circuit 14 obtained by multiplying the signals S11 and S12, and the ground level (0 level) is the signal S1.
1, S12 is GND11, and the signal S13 is GND12. The output signal S13 of the demodulation circuit 14 is the basic signal S1.
AM detection is performed at a frequency twice that of 1, and a voice signal is obtained by integrating this signal S13.

FIG. 2 is a structural explanatory view showing another embodiment of the present invention. That is, the circuit of FIG. 1 and the circuit of FIG.
7 is a circuit configured to be switched, and this circuit enables switching between FM detection and AM detection using the same demodulation circuit 14. In the figure, 13 is a discriminator.

As described above, it is possible to switch between FM detection and AM detection of a voice signal with one pre-stage amplifier and one SAW filter and one IF IC.

[0016]

As described above, according to the present invention, the AM
The audio component obtained from the intermediate frequency signal of the television signal composed of the modulated audio signal and the video signal and the basic signal with the amplitude limited of this audio component are multiplied in the same phase and demodulated to obtain a signal for FM detection. AM detection can be performed using a demodulation circuit including a multiplication circuit, the number of components can be reduced, and switching between FM detection and AM detection can be performed using the same demodulation circuit.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of the present invention.

FIG. 2 is a structural explanatory view showing another embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a configuration of a conventional television receiver.

FIG. 4 is an explanatory diagram showing a configuration of a conventional television receiver.

FIG. 5 is a waveform diagram for explaining the operation of the demodulation circuit including the multiplication circuit according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Receiving antenna, 2 ... Tuner, 3 ... Preamplifier and SAW filter, 4 ... IF IC, 6 ... AM detection circuit,
8 ... SIF filter, 9 ... Voice trap, 11 ... Limiter, 13 ... Discriminator, 14 ... Demodulation circuit, 17
…switch.

Claims (3)

[Claims] 1. A frequency conversion means for receiving a television signal composed of an AM-modulated audio signal and a video signal and converting it into an intermediate frequency signal, and an audio component from the intermediate frequency signal converted by the frequency conversion means. A voice component extracting means, an amplitude limiting means for limiting the amplitude of the voice component extracted from the voice component extracting means, and an output signal from the amplitude limiting means and a voice component extracted from the voice component extracting means. A television receiver comprising demodulation means. 2. A tuner for receiving a television signal composed of an AM-modulated audio signal and a video signal and converting it into an intermediate frequency signal, and a SIF filter for extracting an audio component from the intermediate frequency signal converted by the tuner, A television receiver comprising a limiter for limiting the amplitude of the audio component extracted from the SIF filter, and a demodulation circuit for multiplying the output signal from the limiter and the audio component extracted from the SIF filter. . 3. A frequency converting means for receiving a television signal composed of an AM-modulated audio signal and a video signal and converting it into an intermediate frequency signal, and extracting an audio component from the intermediate frequency signal converted by the frequency converting means. Audio component extracting means, amplitude limiting means for limiting the amplitude of the audio component extracted from the audio component extracting means, phase shifting means for shifting the phase of the output signal from the amplitude limiting means, and the phase shifting means Selecting means for selecting either the output signal of the above or the voice component extracted from the voice component extracting means, and a demodulating means for multiplying the signal selected by the selecting means and the output signal from the amplitude limiting means. A television receiver comprising: