JPS641859B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a pickup circuit for reproducing information on a video disc in a capacitive video disc player.

<Prior Art> Conventionally, a circuit shown in FIG. 1 has been employed as a circuit for picking up signals recorded on a capacitive video disk.

In the figure, variable capacitance 1 equivalently represents the capacitance created by the pit formed on the disk and the electrode of the pick-up needle, and changes depending on the shape of the pit. A tuning coil 2 is connected in parallel with this equivalent variable capacitor 1 to form a parallel resonant circuit 3. 4 is a reference oscillator (CSC) of a predetermined frequency; 5 is a coupling coil; the oscillation output from the reference oscillator 4 is supplied to the resonance circuit 3 via the coupling coil 5; The oscillation frequency of the reference oscillator 4 is set at an appropriate position on the slope of the resonant frequency characteristic waveform, as indicated by f ₀ in FIG. 2 showing the resonant frequency characteristic of the resonant circuit 3. 6 is a pickup coil that picks up the amplitude modulation (AM) output from the resonant circuit 3; 7 is a pickup coil that picks up the amplitude modulation (AM) output from the resonant circuit 3;
The detection diodes forming the AM detection circuit 10 are connected in the forward direction.

A preamplifier 11 amplifies the detection output of the detection circuit 10.

In this pickup circuit, when an oscillation signal of frequency _f0 is supplied from the oscillator 4 to the resonance circuit 3 via the coupling coil 5, the shape of the pit changes as the disk moves, that is, the capacitance value of the variable capacitor 1 changes. The resonant frequency characteristic of the resonant circuit 3 is the second
The resonance frequency changes from the solid line 12 to the broken line 13 in the figure, and the resonant frequency shifts by the amount indicated by the arrow. As the disk rotates, the pick-up coil 6 amplitude-modulates the carrier wave of frequency f ₀ according to the signal recorded on the disk in advance, as shown in FIG. 3a, and picks it up. . This picked up amplitude modulation signal is demodulated (detected) by an AM detection circuit 10 consisting of a detection diode 7, a resistor 8 and a capacitor 9, and is amplified by a preamplifier 11 to produce a demodulated signal as shown in FIG. 3b. The output becomes _V0 . This output signal V ₀ corresponds to a signal (mostly an FM signal) recorded on the disc.

<Problem> By the way, in a pickup circuit like the one shown in Figure 1, if a high-energy interference wave with a frequency _f1 , which is close to the reference oscillation frequency _f0 , enters the player from the outside, the difference between the reference oscillation frequency _f0 and the Beat (f
= f ₀ to _{f 1} ), a beat component is mixed into the detected output V ₀ , and unnecessary components other than the signal originally recorded on the disk appear. In other words, it may cause striped interference on the screen, noise may appear in the audio, or tracking disturbances may occur due to the tracking signal recorded on the disk matching the beat component, which may indicate that the video disk is normal. Functions as a player are hindered.

<Object of the Invention> The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a pickup circuit that is not affected by external disturbances and can perform normal player functions.

<Disclosure of the Invention> That is, in the present invention, beat disturbance (f= _f0 to _f1 ) is generated between the external disturbance frequency _f1 and the reference oscillation frequency _f0 .
When this occurs, the frequencies of both the reference oscillator and the resonant circuit are moved by the same frequency in the same direction to avoid the occurrence of beat disturbance.

<Example> Hereinafter, the present invention will be explained with reference to Examples.

FIG. 4 shows a pickup circuit of one embodiment.
Components designated by reference numerals 1 to 11 in FIG. 4 are similar to those in FIG. 1, and the circuits constituted by these pick up signals on the disk. Here, in addition to the above circuit, there is also a beat disturbance detection circuit 14 that detects the presence or absence of a beat disturbance wave between an external disturbance signal and a reference oscillation signal, and when a beat disturbance wave of a predetermined value or more is detected by this detection circuit 14, resonance occurs. A frequency floating circuit 15 is provided for shifting both the resonant frequency of the circuit 3 and the oscillation frequency of the reference oscillator 4 by the same frequency in the same direction.

In the pickup circuit of the above embodiment, a frequency f ₁ close to the reference oscillation frequency f ₀ of the reference oscillator 4 is input from the outside.
When high-energy interference waves come in,
Beat interference (f = f ₀ ~ _{f 1} ) occurs between this external disturbance signal and the reference oscillation signal, and the beat interference wave is mixed into the detection output V ₀ , but at this moment, this beat interference wave becomes beat interference. It is detected by the detection circuit 14, and based on this detection output, the frequency floating circuit 1
5 is driven, and at this time, the resonant frequency of the resonant circuit 3 and the oscillation frequency of the reference oscillator 4 are the same frequency △f in the same direction, that is, downward, as shown in FIG.
are moved respectively.

As a result, the detection output V ₀ derived through the detection circuit 10 and the preamplifier 11 is not affected by the operation of the frequency floating circuit 15, but the beat mixed in the detection output ₀ at this time is The components are drastically reduced as the reference oscillation frequency is shifted, and the pick-up circuit outputs only the pick-up reproduction signal from which the beat interference waves have been completely removed.

<Effects> As described above, the pickup circuit for a video disc player of the present invention includes a beat disturbance detection circuit that detects beat disturbance between an external disturbance signal and a reference oscillation signal, and a detection output derived from this detection circuit. Since a frequency floating circuit is added that moves the resonant frequency of the resonant circuit and the oscillation frequency of the reference oscillation circuit by the same frequency in the same direction when It is possible to remove only the beat interference waves without affecting the

Furthermore, according to the present invention, as is clear from the above, it is possible to completely eliminate interference waves, and therefore, it is extremely effective against mutual interference between multiple video disc players with varying characteristics, such as during adjustment on a mass production line. It is valid.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional pick-up circuit, Fig. 2 is a diagram showing the resonant frequency characteristics of a resonant circuit and its changes, and Fig. 3 is a waveform diagram showing a pick-up signal. b shows the signal after it has been AM detected. FIG. 4 is a circuit diagram showing one embodiment of the present invention, and FIG. 5 is a diagram showing the resonant frequency characteristics of the resonant circuit in the same embodiment. 1...Variable capacitance equivalent to the capacitance created by the pick and pick-up needle electrodes, 3...Resonance circuit, 4...Reference oscillation circuit, 10...First AM detection circuit, 14...Beat disturbance Detection circuit, 15...
Frequency floating circuit.

Claims (1)

[Claims] 1. A pickup circuit for reproducing a signal recorded as a capacitance change on a video disk, comprising: a resonant circuit including the capacitance of the video disk, a reference oscillation circuit that supplies a reference oscillation signal to this resonant circuit, and the resonant circuit. a detection circuit for detecting the recording signal obtained through the oscillation; a beat disturbance detection circuit for detecting beat disturbance between the signal mixed by external disturbance and the reference oscillation signal; and a detection output derived from the detection circuit. A pickup circuit for a video disc player, comprising: a frequency floating circuit that moves the resonant frequency of the resonant circuit and the oscillation frequency of the oscillation circuit by the same frequency in the same direction, thereby preventing beat disturbance due to external disturbances.