JPS6253089A - Modulation circuit - Google Patents

Abstract

PURPOSE:To prevent the generation of deterioration in hue die to the shift of color difference signal and to faithfully reproduce a color video by inserting a delay circuit in the input-side of a sound modulator, thereby making coincide the carrier wave phases of the outputs from the sound modulator and a video modulator. CONSTITUTION:The carrier wave output from a carrier wave generating circuit 1 having a mono-phase output is amplitude-modulated by the video modulator 3 using a video signal 2a inputted from a signal input terminal 2, and goes to a video modulation output 11 to be inputted to a modulation wave synthesizing circuit 6. Also the said output from the circuit 1 goes through the delay circuit 7, and amplitude-modulated in the sound modulator 5 using a 4.5MHz FM sound signal 4a inputted from a signal input terminal 4, and goes to a sound modulation output 12, and inputted to the circuit 6. By adjusting the said delay circuit 7, the video modulation output 11 and the unnecessary carrier wave phase outputted from the voice modulator 5 are made coincide.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a modulation circuit, and in particular to a modulation circuit for converting video and audio signals reproduced from a video tape recorder into a channel carrier frequency of a home television receiver. Regarding circuits.

(4!t Required) The present invention provides a modulation circuit that modulates two different signals in respective modulators using the output of a carrier wave circuit having a single phase output, and synthesizes the output signals to obtain a modulated output. By connecting a delay circuit between the output of the carrier wave circuit and the input of one of the modulation circuits and matching the carrier phases of the two modulator outputs, it is possible to eliminate color difference signal shift in phase modulation signals, especially color television signals. This eliminates the deterioration in color tone due to color distortion and improves the fidelity of color images.

[Conventional technology]

FIG. 2 is a block diagram showing an example of such a conventional modulation circuit. The video signal 2a is inputted from the carrier wave generation circuit 1 of the television video carrier wave (91.25 MHz in Japan's first channel) and the video signal input terminal 2, and amplitude modulation is performed, resulting in the video modulation output shown in Fig. 3. FM audio signal 4a with a carrier wave of 4.5M) Iz is input from the video modulator 3 and audio signal input terminal 4 to obtain 1), carrier wave suppression amplitude modulation is performed, and audio modulation output (91 .25±4.5MHz) 12, and the carrier wave input terminals of the video modulator 3 and the audio modulator 5 are both connected to the carrier wave output terminal of the video carrier generation circuit l, as shown in FIG. A modulated signal output 6a is obtained by combining the video modulated output 1) and the audio modulated output 12 shown at the modulated synthesis output terminal 6. In this way, the output signal from the video tape recorder was of the same type as the television broadcast wave, and could be reproduced on a home television receiver.

[Problem that the invention seeks to solve]

In the conventional modulation circuit described above, the audio modulation output 12 of the audio modulator 5 uses a carrier wave suppression method, so ideally no carrier wave is output. However, in reality, the active components that make up the modulator
Due to the matching of the passive elements, the unnecessary carrier wave 13 shown in FIG. 3 is outputted, albeit slightly. The carrier wave is output from the carrier wave generation circuit 1 with a single phase output, but since it passes through the video modulator 3 and the audio modulator 5, which have different characteristics, the carrier wave is output at the modulation output end due to the difference in the time constant of both receivers. Generates a phase difference between carrier waves. As a result, during output synthesis, the video modulated output 1) shown in FIG. 3 undergoes phase modulation by the unnecessary carrier wave 13, and as a result, it is transmitted with phase modulation during color television broadcasting. Similarly, the color subcarriers are also subjected to phase modulation.

As shown in Figure 4, the color subcarrier of a color television is represented by a vector combination of R-Y and B-Y color difference signals, and OA and OB are determined from OC during normal operation. When the color subcarrier overlaps the unnecessary carrier, the color difference signal 04 decreases to OA', OB increases to OB', and becomes R-
There was a drawback that the ratio of Y and B-Y changed, resulting in a change in color tone. Conventionally, measures have been taken to prevent the generation of unnecessary carrier waves, such as separating the power supply wiring connected to the video modulator 3 and audio modulator 5 and eliminating common impedance. The effect was not sufficient.

An object of the present invention is to provide a modulation circuit that can prevent the deterioration of color tone due to shifts in color difference signals and improve the fidelity of reproduced color images by eliminating the above-mentioned drawbacks.

[Means for solving problems]

The present invention provides a carrier wave generation circuit (1) having a single phase output.
and a first modulator (3) and a second modulator (4) that modulate the first signal (2a) and second signal (4a) respectively inputted by the output of this carrier wave generation circuit, and this first modulator. a delay circuit (7) connected between the output of the carrier generation circuit and the input of the second modulator; It is characterized by

[For production]

The present invention adjusts the delay circuit to match the phase of unnecessary carrier waves appearing in the video modulation output and the audio modulator output frequency component.
The equivalent phase modulation angle Δθ of the color subcarrier caused by the unnecessary carrier wave, which was conventionally present, can be made zero, so even if there is an unnecessary carrier wave, the ratio of the B-Y component and the R-Y component will not change, so the color image The color tone does not deteriorate, and image fidelity can be improved.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In this embodiment, a video modulator 3 as a first modulator inputs a video signal 2a to a signal input terminal 2 and performs amplitude modulation. ,
The audio modulator 5 as a second modulator has a signal input terminal 4.
A 4.5 MHz FM audio signal 4a is inputted to the 4.5 MHz FM audio signal 4a, and carrier suppression amplitude modulation is performed. The carrier wave output of the carrier wave generation circuit 1 having a single phase output is connected to the carrier wave input of the video modulation H3 and the input of the delay circuit 7, and the output of this delay circuit 7 is connected to the input of the audio modulator 5, and the video modulation It is constructed by connecting the outputs of the audio modulator 3 and the audio modulator 5 to a modulation/synthesis output terminal 6.

A feature of the present invention is that a delay circuit 7 is provided in FIG.

Next, the operation of this embodiment will be explained with reference to the frequency component diagram shown in FIG. 3 and the color difference signal vector diagram in the NTSC system shown in FIG. 4. In FIG. 3, 8 is a video modulator output frequency component, 9 is an audio modulator output frequency component,
Reference numeral 10 indicates the video/audio synthesis output frequency component, and the delay circuit 7 is adjusted to match the phase of the video modulation output 1) and the unnecessary carrier wave 13.

Then, in the color difference signal vector diagram of FIG. 4, the equivalent phase modulation angle Δθ of the color subcarrier by the unnecessary carrier wave 13, which has conventionally occurred, becomes 0, cc' becomes cc'', and B-
Y component goes from OB to OB'', R-Y component goes from OA to OA
'', and the ratio of the R-Y component to the B-Y component does not change, so even if the unnecessary carrier wave 13 is generated, the color tone does not deteriorate.

〔Effect of the invention〕

As explained above, according to the present invention, when the output signals of two modulators inputting a single-phase carrier wave are combined and used, a delay circuit inserted into the carrier wave input terminal of one modulator is used. By matching the carrier wave phases of the two modulator outputs, it is possible to eliminate deterioration of color tone due to color difference signal shift in phase modulation signals, especially color television signals,
This has the effect of improving the fidelity of color images reproduced from a video tape recorder relative to color images reproduced from radio waves transmitted from broadcasting stations.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a frequency component diagram of one embodiment of the present invention. FIG. 3 is a block diagram showing a conventional example. FIG. 4 shows N for explaining the operation of the conventional example and the embodiment.
A color difference signal vector diagram in the TSC method. l...Carrier wave generation circuit, 2...Video signal input terminal,
2a...Video signal, 3...Video modulator, 4...Video signal input terminal, 4a...FM audio signal, 5...Audio modulator, 6...Modulated wave synthesis output terminal, 6a... Modulation signal output, 7... Delay circuit, 8... Video modulator output frequency component, 9... Audio modulator output frequency component, 1
0...Video/audio synthesis output frequency component, 1)...Video modulation output, 12...Audio modulation output, 13...Unnecessary carrier wave.

Claims (1)

[Claims] (1) A carrier wave generation circuit (1) having a single phase output, and a first modulator (3 ) and a second modulator (4), and means (6) for combining the outputs of the first modulator and the second modulator, the output of the carrier generation circuit and the second modulator A modulation circuit characterized in that a delay circuit (7) is connected between an input of the modulation circuit.