JPH0879635A - Rf modulator - Google Patents

Abstract

PURPOSE: To provide an RF modulator where video quality obtained from RF output is improved by reducing a beat component generated by the carrier of a sound signal. CONSTITUTION: In the RF modulator including a clamp circuit 11 to which a video signal is inputted, a white clip circuit 12 to which an output signal from the clamp circuit is inputted, an FM modulation circuit with sound oscillator 13 to which a monophonic sound signal is inputted, an RF mixer 15 to which signals from the white clip circuit and the FM modulation circuit are inputted and to which an oscillation signal from an RF oscillator 14 is inputted, the RF modulator 10 is constituted so that the sound signal carrier of the FM modulation circuit is turned off by a switch 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention applies a video signal and an audio signal of a VTR device, a BS tuner, a CATV tuner, etc.
The present invention relates to an RF modulator, which is adapted to be converted into an F signal and output to a television receiver or the like, and particularly to an RF modulator compatible with audio multiplexing.

[0002]

2. Description of the Related Art Conventionally, such a voice multiplex compatible RF modulator is constructed, for example, as shown in FIG. That is, in FIG. 4, the RF modulator 1 includes a clamp circuit 2 to which a video signal is input, and the clamp circuit 2
From the white clip circuit 3 into which the signal from the white clip circuit 3 is input, the FM modulation circuit 4 into which the monaural audio signal is input, the signals from the white clip circuit 3 and the FM modulation circuit 4, and a stereo audio signal (sub audio Carrier)
And an RF mixer 6 to which the oscillation signal from the RF oscillator 5 is input.

Of the above circuits, the clamp circuit 2, the white clip circuit 3 to which the signal from the clamp circuit 2 is input, and the FM modulation circuit 4 to which the monaural audio signal is input are incorporated in one IC 7. And I
A drive voltage is supplied by a regulator 8 provided in C.

Further, the FM modulation circuit 4 has an IC 7
An external tank circuit 9 is connected to. The tank circuit 9 is composed of, for example, a parallel circuit of a capacitor and a coil, and has a resonance frequency determined by the capacitor and the coil.

The RF modulator 1 having such a configuration is
By applying a drive voltage to the regulator 8 from the outside, the drive voltage is supplied to each of the circuits 2, 3 and 4. In this state, a video signal and a monaural audio signal among signals from a VTR (not shown) are input to the clamp circuit 2 and the FM modulation circuit 4, respectively. As a result, the video signal is input from the clamp circuit 2 to the RF mixer 6 via the white clip circuit 3. The audio signal is FM-modulated based on the oscillation frequency of the audio oscillator incorporated in the FM modulation circuit 4, and then input to the RF mixer 6. The oscillation frequency of the audio oscillator is determined by the resonance frequency of the external tank circuit 9.

On the other hand, a stereo audio signal which is a sub audio carrier for audio multiplexing is directly input to the RF mixer 6.

Thus, the RF mixer 6, based on the oscillation signal from the RF oscillator 5, the video signal, the monaural audio signal and the stereo audio signal (sub audio carrier).
Are mixed and output as an RF signal.

[0008]

However, in the RF modulator 1 having such a configuration, since the carrier of the monaural audio signal is constantly output in the FM modulation circuit 4, the RF output from the RF mixer 6 is set. As shown in FIG. 5, the output includes a video carrier fp, a monaural audio carrier fs ₁ , a high-fidelity audio carrier fs _2, and a chroma signal fc. For example, three beat components are provided between the video carrier fp and the chroma signal fc. fb ₁ , fb ₂ , f
b ₃ is generated. This beat component fb ₁ , fb ₂ , f
b ₃ is a signal in which a monaural audio carrier fs ₁ , a high-fidelity audio carrier fs _2, and a chroma signal fc are shown on the video carrier fp. That is,
The beat components fb ₁ , fb ₂ and fb ₃ are respectively expressed by the following equations.

[0009] _{fb 1 = fp + (fs 2} -fs 1)

Fb ₂ = fp + (fs ₁ -fc)

It is represented by fb ₃ = fp + (fs ₂ −fc).

Therefore, these beat components fb ₁ and fb
Since both b ₂ and fb ₃ are within the band of the video signal, R
When the video signal is taken out from the F output, there is a problem that the video is disturbed. In particular, of the beat components, the beat components fb ₁ and fb ₂ are the remaining beat components fb.
Since it is relatively large compared to ₃ , there was a problem that the disorder of the image appears remarkably.

In view of the above points, it is an object of the present invention to provide an RF modulator which improves the image quality obtained from the RF output by reducing the beat component generated by the carrier of the audio signal. I am trying.

[0014]

According to the present invention, the above object is to provide a clamp circuit to which a video signal is input, a white clip circuit to which an output signal from the clamp circuit is input, and a monaural audio signal. FM modulator circuit with audio oscillator, the white clip circuit and F
In an RF modulator including an RF mixer to which a signal from the M modulation circuit is input and an oscillation signal from the RF oscillator is input, the audio signal carrier of the FM modulation circuit is turned off. , RF modulators.

The RF modulator according to the present invention is preferably such that when the sound signal carrier of the FM modulation circuit is turned off,
This is performed by a switch connected to the audio signal carrier off terminal of the M modulation circuit.

The RF modulator according to the present invention is preferably such that when the voice signal carrier of the FM modulation circuit is turned off,
This is performed by a switch provided on the connection line with the tank circuit that determines the modulation frequency of the M modulation circuit.

[0017]

According to the above construction, since the audio signal carrier is turned off at the time of input of the audio multiplex broadcast in the FM modulation circuit to which the monaural audio signal is input, the carrier of the monaural audio signal is not input to the RF mixer. Therefore, the beat component related to the carrier of the monaural audio signal is not generated, and the beat signal in the band of the video signal can be reduced.
Therefore, the image due to the RF output is not disturbed by the beat signal, and the image quality can be improved.

If the voice signal carrier of the FM modulation circuit is turned off by a switch connected to the voice signal carrier off terminal of the FM modulation circuit, the conventional R signal is used.
It can be configured simply by connecting a switch for turning off the voice signal carrier to the F modulator.

When the voice signal carrier of the FM modulation circuit is turned off by a switch provided in the connection line with the tank circuit that determines the modulation frequency of the FM modulation circuit, the FM modulation of the conventional RF modulator is performed. It can be constructed by a simple operation of providing a switch between the circuit and the tank circuit.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. FIG. 1 shows an embodiment of an RF modulator according to the present invention.
Is a clamp circuit 11 to which a video signal is input, a white clip circuit 12 to which a signal from the clamp circuit 11 is input, an FM modulation circuit 13 to which a monaural audio signal is input, and the white clip circuits 12 and FM. An RF mixer 15 to which a signal from the modulation circuit 13 is input, a stereo audio signal (sub audio carrier) is input, and an oscillation signal from the RF oscillator 14 is input.
It consists of and.

Of the above circuits, the clamp circuit 11, the white clip circuit 12 to which the signal from the clamp circuit 11 is input, and the FM modulation circuit 13 to which the monaural audio signal is input are incorporated in one IC 16. In addition, a drive voltage is supplied by a regulator 17 provided in the IC 16.

Further, the FM modulation circuit 13 has an IC
An external tank circuit 18 is connected to 16.
The tank circuit 18 is composed of, for example, a parallel circuit of a capacitor and a coil, and has a resonance frequency determined by the capacitor and the coil.

The above-mentioned configuration is similar to that of the conventional RF modulator 1 shown in FIG. 4, but in the RF modulator 10 according to the embodiment of the present invention, the above-mentioned FM is further added.
For the voice carrier off terminal 13a of the modulation circuit 13,
The switch 19 is connected. Further, the switch 19 has a contact on the other side grounded.

The RF modulator 10 according to the present invention is configured as described above, and by applying a driving voltage to the regulator 17 from the outside, each circuit 11,
A drive voltage is supplied to 12 and 13. In this state, the video signal and the monaural audio signal among the signals from the VTR (not shown) are respectively clamp circuit 11
And the FM modulation circuit 13. As a result, the video signal is input from the clamp circuit 11 to the RF mixer 15 via the white clip circuit 12. The monaural audio signal is FM-modulated based on the oscillation frequency of the audio oscillator incorporated in the FM modulation circuit 13 and then input to the RF mixer 15. The oscillation frequency of the sound oscillator is determined by the resonance frequency of the tank circuit 18 attached externally.

On the other hand, the stereo audio signal which is the sub-audio carrier for audio multiplexing is directly input to the RF mixer 15.

Thus, the RF mixer 15, based on the oscillation signal from the RF oscillator 14, outputs the video signal,
A monaural audio signal and a stereo audio signal (sub audio carrier) are mixed and output as an RF signal.

Here, the switch 1 is used when inputting the audio multiplex broadcast.
When 9 is turned off, the carrier of the monaural audio signal of the FM modulation circuit 13 is turned off. Therefore, the RF mixer 15
Since the carrier of the monaural audio signal is not input to the RF mixer 15, the RF output output from the RF mixer 15 includes the video carrier fp, the hi-fi audio carrier fs ₂ and the chroma signal fc as shown in FIG. Only a sufficiently small beat component fb ₃ is generated between the carrier wave fp and the chroma signal fc. Thus, the beat component contained in the RF output can be sufficiently reduced.

FIG. 3 shows another embodiment of the RF modulator according to the present invention. That is, in FIG. 3, the RF modulator 20 is replaced by the F modulator instead of the switch 19 of FIG.
A switch 21 is provided between the M modulation circuit 13 and the tank circuit 18.
The RF modulator 10 has the same configuration as that of the RF modulator 10 of FIG.

According to this structure, the FM modulation circuit 1 is turned on by turning off the switch 21 at the time of input of the audio multiplex broadcast.
In No. 3, the resonance frequency of the tank circuit 18 is not input. Therefore, the carrier of the monaural audio signal of the FM modulation circuit 13 is turned off. Therefore, as in the case of the RF modulator 10 of FIG. 1, since the carrier of the monaural audio signal is not input to the RF mixer 15, the RF output output from the RF mixer 15 is as shown in FIG.
The video carrier fp, the hi-fi audio carrier fs ₂ and the chroma signal fc are included, and only a sufficiently small beat component fb ₃ is generated between the video carrier fp and the chroma signal fc. Thus, the beat component contained in the RF output can be sufficiently reduced.

[0030]

As described above, according to the present invention, in the FM modulation circuit to which a monaural audio signal is input, the audio signal carrier is turned off at the time of input of the audio multiplex broadcast.
The carrier of the monaural audio signal is not input to the F mixer. Therefore, the beat component related to the carrier of the monaural audio signal is not generated, and the beat signal in the band of the video signal can be reduced. Therefore, the image due to the RF output is not disturbed by the beat signal, and the image quality can be improved.

Thus, according to the present invention, it is possible to provide an extremely excellent RF modulator that improves the image quality obtained from the RF output by reducing the beat component generated by the carrier of the audio signal. become.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an RF modulator according to the present invention.

FIG. 2 is a graph showing frequency components of RF output by the RF modulator of FIG.

FIG. 3 is a schematic perspective view showing another embodiment of the RF modulator according to the present invention.

FIG. 4 is a schematic perspective view showing an example of a conventional RF modulator.

5 is a graph showing frequency components of RF output by the RF modulator of FIG. 1. FIG.

[Explanation of symbols]

 10, 20 RF modulator 11 Clamp circuit 12 White clip circuit 13 FM modulator circuit with oscillator for voice 14 RF oscillator 15 RF mixer 16 IC 17 Regulator 18 Tank circuit 19, 21 Switch

Claims (3)

[Claims] 1. A clamp circuit to which a video signal is input,
A white clip circuit to which an output signal from the clamp circuit is input, an FM modulation circuit with an audio oscillator to which a monaural audio signal is input, and an RF oscillator to which signals from the white clip circuit and the FM modulation circuit are input And an RF mixer to which an oscillating signal is input, wherein the audio signal carrier of the FM modulation circuit is turned off. 2. An audio signal carrier of the FM modulation circuit is turned off by a switch connected to an audio signal carrier off terminal of the FM modulation circuit.
The RF modulator according to claim 1. 3. An audio signal carrier of the FM modulation circuit is turned off by a switch provided in a connection line with a tank circuit that determines a modulation frequency of the FM modulation circuit. An RF modulator as described in 1.