JPH0262910B2 - - 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, thereby producing concentric or vortex-shaped pits on the recording disk. (dents) are formed by forming rows.

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 not only the _fV component and _fA component but also the beat phenomenon.
Two beat 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 composite vector 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 multi-recorded information reproducing apparatus that reduces spurious interference caused by cross-modulation between an audio carrier and a video carrier as much as possible.

The reproducing apparatus according to the present invention performs the following steps when reproducing a recording medium in which another information signal is superimposed on a carrier signal that is angularly modulated by a predetermined information signal.
The angle-modulated carrier signal in the output signal is phase-modulated in accordance with other information signals in the reproduced signal, and this carrier signal caused by cross-modulation of the other information signal and the angle-modulated carrier signal is It is characterized by substantially canceling the phase modulation component of the signal.

The present invention will be explained in detail below using the drawings.

FIG. 3 is a block diagram of an embodiment of the present invention;
The reproduced RF signal by pick-up consists of a video carrier component (f _V ′) and an audio carrier component (f _A ).
and are applied to extractors 2 and 3, which separate them, respectively.
These extractors 2 and 3 are constituted by BPF (band pass filter). The video carrier component from the extractor 2 is input to a phase modulator 6 via a delayer 4 and a limiter 5. The audio carrier component is level-adjusted by a level adjuster 7, and is input to a phase modulator 6, which modulates the phase of the video carrier component. This phase modulated output is applied to the FM detector 8 and becomes a video reproduction signal.

Extraction output f _V ′ in video carrier extractor 2
As explained in Figure 2b, phase modulation (δ) is caused by the level difference between the upper and lower sideband components (f _V ±f _A ) due to cross modulation between the audio carrier f _A and video carrier f _V . is recieving. Since this phase modulation component can be considered to have the same angular frequency w _A as the audio carrier component (f _A ) based on the video carrier component (f _V ), the extracted output
f _V ′ is expressed by the following formula.

f _V ′=Ksin (w _V t+βsin w _A t+θ) (1) Here, K and β are constants, and θ indicates a constant phase. Therefore, the phase modulation component δ in equation (1)
(t)=βsin w _A If the output f _V ' of the extractor 2 is subjected to phase modulation processing so as to cancel t, the interference caused by the above-mentioned cross modulation can be eliminated.

Here, the extracted output (f _A ) by the audio carrier extractor 3 is expressed as f _A =ksin w _A t (2), so the level is adjusted by the level adjuster 7, and k=- If the output of the level adjuster 7 is -βsin w _A t, then if the input f _V ′ of the modulator 6 is phase-modulated by this signal, f _V ′=Ksin(w _V t+βsinw _A t+θ−βsinw _A t)=
Ksin(w _V t+θ) (3) Thus, the phase modulation component δ(t) due to cross modulation can be eliminated.

FIG. 4 is a diagram showing a specific example of the phase modulator 6 in the block of FIG. 3, in which the video carrier signal f _V ', which is a reproduced RF signal, is vibration-limited by the limiter 5 (see FIG. 3) and converted into a rectangular wave signal. The phase modulator 6 is n (n is a natural number) cascaded delayed multivibrators 6-1 to 6.
−n is input to the first stage circuit. Final stage circuit 6
The output of -n is input to the FM detector 3 and subjected to FM detection, and is demodulated into, for example, a color video signal by passing through the LPF 4.

Daylaid multivibrator 6-1~6-n
Each rises (falls) with a certain delay time τ ₀ in response to the rise (fall) timing of the input pulse, and also with a delay time τ 0 in response to the rise (fall) timing of the input pulse. It performs an operation such as falling (rising) after reaching ₀ , and a well-known configuration is used. For example, as shown in the figure, _a constant current source consisting of _a transistor Q ₃ and a resistor R ₁ is connected to the common emitters of a pair of differentially connected transistors Q ₁ and Q ₂ . There is a capacitive element _C0 between the collectors that determines the circuit time constant.
is provided. Switching transistors Q ₄ and Q ₄ are connected to the collectors of transistors Q 1 and Q ₂ , respectively.
Q ₅ is provided in a cascade connection with these transistors Q ₁ and Q ₂ , and both transistors
Positive feedback switching transistors Q ₆ and R ₇ whose base inputs are the collectors of Q ₄ and Q ₅ are provided.
The emitters of both transistors Q ₆ and Q ₇ are connected to the bases of transistors Q ₅ and Q ₄ , respectively.
A circuit power supply +V _CC is supplied to the collectors of both transistors Q ₆ and Q ₇ .

In order to determine the collector potential of transistors Q ₄ and Q ₅ , a bias generation circuit consisting of transistors Q ₈ to Q ₁₀ and resistors R ₂ and R ₃ is provided, and this bias voltage value is one element that determines the delay time of the circuit. _{In order to}
A temperature compensation circuit consisting of ~ _R7 is added.
Other daylaid multivibrators 6-2 to 6-
The structure is exactly the same for n, and a signal corresponding to the audio carrier signal component (f _A ) in the reproduced signal is applied to the base of transistor Q ₃ of the current source in each circuit, and the current I of the current source is ₀ is controlled according to this signal.

FIG. 5 is an operating waveform diagram of the circuit 6-1 in FIG. 4, and A and B are forward and reverse rectangular waves of the reproduced RF video carrier signal by the limiter 5, and are input to both bases of the differential transistors Q ₁ and Q ₂ . , and C and D are the collector waveforms of both transistors Q ₁ and Q ₂ . E and F are a pair of output waveforms of positive and opposite phases, and represent the waveforms of the bases of transistors Q ₄ and Q ₅ or the waveforms of transistors Q ₇ and Q ₆ . That is, with the illustrated configuration, a pulse delay circuit having a predetermined delay time τ ₀ in response to the transition timing of the input signal can be obtained.

Here, the delay time τ ₀ of the delayed multivibrator is expressed as 2C ₀ V ₀ /I ₀ . Here, C ₀ is the capacitance of the capacitive element, I ₀ is the current source current, and V ₀
is the voltage between the bases of transistors Q ₁₁ and Q ₁₂ of the temperature compensation circuit, and determines the collector potential of transistors Q ₄ and Q ₅ .

If the value of the audio carrier signal (f _A ) becomes small, the current I ₀ of the current source becomes small, and therefore the delay time τ ₀ becomes large. That is, as shown in FIG. 5, the delay amount, which was τ ₀ , changes to τ ₁ . This is because the charging/discharging current value of the capacitor C ₀ changes and the circuit time constant changes.

The delay time amount τ ₀ is not only used to control I ₀ but also to control C ₀ and V ₀
Therefore, as shown in FIG. 6, the capacitance C ₀ that determines the time constant can be actively controlled. That is, variable capacitance diodes (varicaps) _D1 and _D2 are equivalently inserted in parallel to capacitor _C0 , and the capacitance value is controlled by an audio carrier signal ( _fA ). Furthermore, V ₀ may be controlled by known means.

Daylaid multivibrator 6-1~6-n
The reason why a plurality of FM-RF signals are connected in cascade is to increase the control width (τ 0 ) since it is difficult to obtain a large control width (τ ₀ ) with a single-stage circuit because the FM-RF signal has a high frequency. One or more stages may be used depending on the amount of control width and the characteristics of the element. Furthermore, since the delayed multivibrator is a digital signal processing circuit, any change in the amplitude of the input signal does not appear in the output, so it can be said to have a limiter effect. Therefore, the limiter circuit 5 shown in FIG. 3 may be omitted.

FIG. 7 is a vector diagram showing the influence of cross-modulation shown in FIG. 2 in more detail. Parts equivalent to those in FIG. 2 are designated by the same reference numerals, and their explanation will be omitted. In A, the vector component f _VA is a composite vector of upper and lower sideband components f _V ±f _A due to cross modulation, and the in-phase and quadrature components of this composite vector f _VA with respect to the video carrier component f _V are respectively indicated by the dotted lines.
It is indicated by f _VAM and f _VPM . FIG. 3B shows a vector waveform when the vector waveform in FIG. f _VL is the amplitude limit vector of the ideal video carrier component f _V that is not subjected to cross-modulation, (f _V ±f _A ) _L is the amplitude limit vector of both upper and lower sideband components due to cross-modulation.
f _VPML is a composite vector of vector components (f _V ±f _A ) _L , and is a component equivalent to the orthogonal component f _VPM in Figure A.
Then, f′ _VL is a composite vector of components f _VL and f _VPML , and this is subjected to phase modulation (δ).

In the present invention, in order to remove this phase modulation amount δ, the phase modulator 6 shown in FIG. f _VL , (f _V ±f _A ) This means that _{the phase of L} is shifted counterclockwise by δ while maintaining the same phase relationship. However, when a circuit having a delayed multivibrator configuration as shown in FIG. 4 is used as the phase modulator 6, its frequency versus phase characteristics are not equal but vary linearly, as shown in FIG. 8. For example, if the phase change for the video carrier component (f _V ) varies within the range of + _n to _-n , then
For the upper sideband component (f _V + f _A ) due to cross modulation, it varies in the range + _n + Δ to − _n − Δ, and for the lower side band component ( f _V − f _A ) it varies from + _n − Δ to - has a fluctuation range of _n + Δ.

Therefore, when the video carrier component (f _VL ) has a phase variation of δ, the phase variation of both the upper and lower sideband components (f _V ±f _A ) becomes δ±Δδ. That is,
The circuits (6-1 to 6-n) in FIG. 4 cannot uniformly give a phase shift of δ to each signal component f _VL , (f _V ±f _A ) _L shown in FIG. 7B. become. This means that each component f _VL , (f _V ±f _A ) _L in Figure 7B does not uniformly rotate counterclockwise by δ, thus completely eliminating phase fluctuations due to cross modulation. However, since the value _Δn in FIG. 8 is extremely small and can be virtually ignored, there is no practical problem.

FIG. 9 is a circuit block diagram of another embodiment of the present invention, in which the modulation signal of the phase modulator 6 in FIG. The wave is detected by a detector 9, its level is adjusted by a level adjuster 10, and the output is used as a modulation signal.

In other words, in the FM detection output, the phase modulation component due to cross modulation is obtained in the waveform β sin w _A t (see equation (1)), so extract the angular frequency w _A .
The BPF-configured detector 9 detects this component βsin w _A t, which causes the phase modulator 6 to
FM/RF signal, that is, Ksin (w _A t+βsin w _A t+
θ) can be phase modulated to cancel the phase term β sin w _A t.

However, this example is effective when the video signal does not include the angular frequency _wA component at all, or even if it does, it is extremely small. in other cases
This is not preferable because the signal component _wA is detected and canceled, but in such a case, the interference due to cross modulation is not so noticeable that it is not necessary to compensate.

As described above, according to the present invention, cross-modulation interference can be removed very easily, and in particular, if a delayed multivibrator is used as a phase modulator, integration is possible and the device becomes compact.

[Brief explanation of drawings]

Fig. 1 is a frequency spectrum of a reproduced RF signal by pickup, Fig. 2 is a diagram showing the mode of cross modulation in vector form, Fig. 3 is a block diagram of an embodiment of the present invention, and Fig. 4 is a diagram of Fig. 3. 5 is a diagram showing operation waveforms of each part of the circuit in FIG. 4, FIG. 6 is a diagram showing a partial modification of the circuit in FIG. 4, and FIG. A more detailed vector diagram of the vector diagram in Fig. 8 is a characteristic diagram of the circuit in Fig. 4, and Fig. 9
The figure is a block diagram of another embodiment of the invention. Explanation of the symbols of the main parts, 1... Pick up,
6...Phase modulator, 8...FM detector.

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 angle-modulated by a predetermined information signal and multiplexed thereon, wherein said other information signal in the reproduction signal modulating means for phase-modulating the angle-modulated carrier signal in the reproduced signal according to the angle-modulated carrier signal; A playback device characterized by substantially canceling phase modulation components. 2. The modulating means includes a delayed multivibrator, and uses the angle-modulated carrier signal in the reproduced signal as a trigger input of the delayed multivibrator, and modulates the delayed multivibrator according to other information signals in the reproduced signal. 2. The playback device according to claim 1, wherein the playback device controls the amount of delay of the multivibrator.