JPH0421941B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reproducing apparatus for multiple recorded information, and more particularly to a reproducing apparatus for a video disc by multiple recording of video information and audio information.

When multiplexing video information and audio information and recording them on a video disk, for example, the video signal is used to angle-modulate the carrier signal _fV (phase or frequency modulation), and the audio signal is used to convert the carrier signal fV to another lower frequency carrier signal. f _A is modulated using a predetermined modulation method and the two are superimposed, and the radio frequency (RF) signal obtained in this way is used to optically modulate, for example, a recording laser beam, creating concentric or spiral pits (dents) on the recording disk. ) is formed by forming a column.

To read recorded information from this recording disk,
While rotating the recording disk at a desired number of rotations, a reading laser beam is irradiated and the reflected or transmitted light is detected by a photodetector, or a change in capacitance is detected by an electrode provided on the stylus. This is done by For this purpose, optical pickup devices, capacitive pickup devices, and the like are used. The RF signal reproduced by this pick-up contains _fV and _fA components as well as cross-modulation phenomena.
Two intermodulation components, f _V −f _A and f _V +f _A, occur as upper and lower sidebands of the video signal carrier f _V .

Here, as is well known, in the case of a pick-up, the frequency characteristic generally decreases in the high frequency region, so a difference occurs in the level of the spurious components generated as the above-mentioned two side bands, and as shown in FIG. The relationship is as shown below.

Now, considering these frequency components in vector terms, if the video carrier component f _V is a stationary vector and both sideband component levels are equal, then both sideband components are equal in opposite directions to the video carrier component. Since it rotates at an angular velocity, it becomes as shown in Figure 2a, and the total composite vector is in phase with the video carrier component and only its level changes. Therefore, if the levels of both sideband components are equal, spurious signals caused by the audio carrier act as AM modulation on the video carrier. Therefore, the spurious can be removed by the limiter at the stage before the detection stage.

However, if the upper sideband level decreases due to high-frequency degradation characteristics caused by pickup, the total synthesis belt will have a phase difference δ with respect to the video carrier component, as shown in FIG.
Therefore, the video carrier component is subjected to phase modulation by the spurious component, which cannot be removed by the limiter, and the interference wave is superimposed on the detection output, causing noise on the screen.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reproducing apparatus for multiplexed information in which spurious interference due to cross-modulation between an audio carrier and a video carrier is reduced as much as possible on the reproducing side.

A reproducing apparatus for multiplexed information according to the present invention is an apparatus for reproducing a recording medium on which another information signal is superimposed on a carrier signal angularly modulated by a predetermined information signal, and in which the angular modulation in the reproducing signal is performed. AM-modulating the 90° phase-shifted output of the 90° phase-shifted carrier signal with another information signal in the reproduced signal, the phase with respect to the carrier signal generated by cross-modulation of the other information signal and the angle-modulated carrier signal is The present invention is characterized in that a component substantially equal to the modulation component is generated, and this AM modulation output is subtracted from the carrier signal in the reproduced signal to reduce interference due to cross modulation.

The present invention will be explained below using the drawings.

FIG. 3 is a circuit block diagram of an embodiment of the present invention, in which the RF reproduction signal from the pickup 1 is amplified by the amplifier 2, and then transferred to the video carrier extraction circuit 3.
and are input to the audio carrier extraction circuit 4, respectively. Both extraction circuits are comprised of BPFs (powered pass filters) for separating and extracting the video RF signal _fV and the audio RF signal _fA , respectively. The output of the video carrier extraction circuit 3 is applied to a subtracter 5 and a 90° phase shifter 6, respectively, and the output of the 90° phase shifter 6 is balanced modulated by the output of the audio carrier extraction circuit 4 in a balanced modulator 7. Ru. i.e. playing video
The RF signal becomes an AM (amplitude modulation) signal whose carrier is suppressed by the reproduced audio RF signal.

This balanced modulation output is level-adjusted by a level adjuster 8 and becomes one input of the subtracter 5, where it is subtracted from the reproduced video RF signal. Thereafter, the amplitude is limited by a limiter and input to the FM detector 10, where the video signal is reproduced.

FIG. 4 is a vector diagram of each RF signal for explaining the operation of the circuit of FIG. 3. Parts equivalent to those in FIG. 2 are designated by the same reference numerals, and their explanation will be omitted. As shown in the figure, it is assumed that the reproduced video RF signal component _fV is cross-modulated by the audio RF signal component _fA and becomes _f'V with phase modulation. The vector components f _VAM and f _VPM shown by dotted lines are the composite vector f VA of spurious components f _V + f _A and f _V − _{f A.}
are the in-phase and quadrature components for the video RF component _fV . The in-phase component _fVAM becomes an amplitude modulation component for the video RF component _fV , and the quadrature component _fVPMM becomes a phase modulation component for the video RF component _fV .

In order to reduce or cancel this orthogonal component f _VPM , the reproduced video RF component f' _V (which has been phase modulated by cross-modulation) is phase-shifted by 90 degrees in the π/2 phase shifter 6, and the component f' _V and An orthogonal component f′ _V1 is generated. Since this orthogonal component f′ _V1 is balanced modulated by the reproduced audio RF component f _A , both upper and lower sideband components having frequencies of the sum and difference of f′ _V1 and f _A
f′ _V1 +f _A and f′ _V1 −f _A are obtained as shown in the figure. Since the composite vector component f′ _V1AM of both sideband components is in phase with the reproduced video RF component f′ _V1 , this composite vector component f′ _VV1AM and the previous phase modulation component f _VPM can be considered to be approximately in phase. . This is because the phase variation angle δ can be considered to be minute.

Therefore, if the level adjuster 8 adjusts the level of the composite vector component f' _V1AM to make it approximately equal to the phase modulation component f _VPM , the subtracter 5 adjusts the level of the composite vector component f' V1AM so that the two components f _VPM and f' _V1AM are equal to each other. Since they almost cancel each other out, the output of subtractor 5 contains the video signal.
An amplitude modulation component f _VAM that is in phase with the RF component f _V remains.
This component f _VAM is removed by limiter 9, so
In the FM detection output, cross-modulation interference due to audio RF components is removed or reduced.

As described above, the present invention has the advantage of being able to improve the reproduced image quality with an extremely simple configuration.

[Brief explanation of drawings]

Figure 1 is a diagram showing the frequency spectrum of the reproduced RF signal obtained by picking up a multiplex recording medium.
3 is a vector diagram showing the aspect of cross modulation, FIG. 3 is a block diagram of an embodiment of the present invention, and FIG. 4 is a vector diagram explaining the operation of the block in FIG. 3. Explanation of the symbols of the main parts, 1... Pick up,
3...Video carrier extraction circuit, 4...Audio carrier extraction circuit, 5...Subtractor, 6...π/
2 phase shifter, 7...balanced modulator.

Claims (1)

[Scope of Claims] 1. A reproducing device for reproducing a recording medium in which another information signal is superimposed on a carrier signal that is angle-modulated by a predetermined information signal, and that the angle-modulated carrier signal in the reproduction signal is The 90° phase-shifted output of the carrier signal is amplitude-modulated by the other information signal in the reproduced signal, and the output of the carrier signal generated by cross-modulation of the other information signal and the angle-modulated carrier signal is An apparatus comprising: modulating means for generating a component substantially equal to a phase modulation component; and means for mixing the output of the modulating means and the carrier signal in the reproduced signal to reduce interference due to the cross modulation. 2. The apparatus according to claim 1, wherein the modulating means comprises a carrier suppression type balanced modulator.