JPS5888846A - Pickup circuit of video disk player - Google Patents

Abstract

PURPOSE:To reduce the undesired radiation level of a video disk player, by coupling variable capacity which shows the variation of capacity on the disk to an oscillator which generates the reference oscillating frequency and applying the frequency modulation to the oscillator. CONSTITUTION:A variable capaicty 1 showing the variation of capacity on a disk is coupled to an oscillator 4'. The modulation of frequency is applied to the oscillator 4' in response to the capacity 1 and with use of the reference oscillating frequency as a carrier wave. Then the frequency modulated wave is applied to a parallel resonance circuit 3 via a coupling coil 5. The circuit 3 consists of a fixed capacity 10 and a coil 2, and each value is set so that the FM modulated wave frequency obtained from the oscillator 4' corresponds to the slant part of the resonance characteristics of the circuit 3. Thus the amplitude modulated signal picked up from a pickup coil 6 is demodulated by an AM demodulation circuit consisting of a diode 7, etc. Then the FM signal recorded on the disk is obtained.

Description

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

2. Description of the Related Art A conventional general capacitive video disc player employs a pickup circuit shown in FIG. 1 to pick up signals recorded on a disc. That is, here 1 isometrically represents the variable capacitance including the disk through the tip of the cartridge needle, and a resonant coil 2 is connected in parallel with this variable capacitor 1, thereby forming a parallel resonant circuit 8 together with the variable capacitor 1. There is. 4 is a reference oscillator, and the oscillation output from this oscillator 4 is supplied to the parallel resonant circuit 3 through the coupling coil 5; The oscillation frequency fO of the oscillator 4 is set to be at the slope of the average resonant frequency characteristic of the parallel resonant circuit 3, as shown in FIG.

6 is a pickup coil that picks up the amplitude modulation (AM) output from the resonant circuit 3, and 7 is a diode that, together with a capacitor 8 and a resistor 9, constitutes an -AM demodulation circuit. Here, when a reference oscillation signal is supplied from the reference oscillator 4 to the parallel resonant circuit 8 via the coupling coil 5, the pickup coil 6 generates a signal according to the signal recorded in advance on the disk as shown in am(a). The amplitude modulated signal is picked up and this is passed through diode 7
etc., is demodulated by an AM demodulation circuit consisting of f, (Fig. 3 (1))
A demodulated output as shown in Figure 2 is obtained. This output corresponds to the FM signal recorded on the disc.

By the way, in the above-mentioned pickup circuit, even if the reference oscillator 4 is sufficiently shielded, the variable capacitance 1 is determined by the capacitance including the cartridge needle tip and the disk, and the resonant circuit 3 cannot be sufficiently shielded. figure,
Therefore, the oscillation output supplied to the resonant circuit 3 is largely leaking to the outside from this cartridge mounting portion.

For this reason, it has been extremely difficult to reduce the level of unnecessary radiation in the player. In addition, if this shielding is to be carried out sufficiently, it will not be a sufficient measure unless the disk including the cartridge stylus tip is also shielded, which is difficult due to the structure, and the cartridge stylus tip There was a risk that the signal picked up by the capacitance number between the player and the shield case would be binocularized, making it impossible to function as a player.

Furthermore, metallizing the player's cabinet has a shielding effect to some extent, but on the other hand, the cabinet itself becomes an antenna, so the present invention has been developed with this in mind. The present invention provides a pickup circuit that can reduce unnecessary shots in a player.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention shown in the drawings will be described below. FIG. 4 shows one embodiment of the present invention, in which the first
Parts that are the same as those in the figure are given the same reference numerals. Here, the variable capacitor 1 representing the capacitance change on the disk is the oscillator 4.
' side, and this oscillator 4' has a reference oscillation frequency f
Using o as a carrier wave, frequency modulation is applied according to the variable capacitance l. This frequency modulated wave is then applied to the parallel resonant circuit 3 via the coupling coil 5. Here, parallel resonant circuit 3
consists of a fixed capacitor 10 and a coil 2, and has multiple values set so that the frequency of the FM modulated wave obtained from the oscillator 4' falls on the slope of the resonance characteristic of the resonance circuit 3, as shown in FIG. . Therefore, in this case, a prefectural modulation signal as shown in FIG. 3(a) is picked up from the pickup coil 6, and this is demodulated by an AM demodulation circuit consisting of a diode 7, etc., and as a result, the FM signal previously recorded on the disk is is obtained.

As described above, according to the pickup circuit of this embodiment, the variable capacitor 1 including the car) IJ needle tip is the oscillator 4'
This part is a part of the oscillator where the oscillation force is relatively low, and on the other hand, the parallel resonant circuit 3 can be sufficiently shielded, so there is no possibility that the oscillation force at a higher level than the cartridge mounting part will leak to the outside. There isn't.

According to the present invention, as described above, a variable capacitor representing a capacitance change on the disk is coupled to an oscillator for generating a reference oscillation frequency, and frequency modulation is applied by the capacitance change on the disk using the reference oscillation frequency as a carrier wave. Since this modulated wave is supplied to a fixed resonant circuit to obtain an amplitude modulated output, the leakage of the oscillation output from the cartridge mounting part is relatively small, and the unnecessary radiation level from the video disc player can be reduced. is possible.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of a conventional pickup circuit, FIG. 2 is a resonance characteristic diagram of the same circuit, and FIG. 8(a). (b) is a signal waveform diagram in the same circuit, FIG. 4 is a circuit configuration diagram of one embodiment of the present invention, and FIG. 5 is a resonance characteristic diagram in the same embodiment. 1...Variable capacitance, 3...Resonance circuit, 4'...
Oscillator, 5...coupling coil, 6...pink-up coil. Agent Patent Attorney Aihiko Fukushi Figure 1 f. Figure 2 tσ (b) Figure 3 O Figure 5

Claims (1)

[Claims] 1. A circuit for reproducing an FM signal recorded on a capacitance type video disc by changing the capacitance, in which a variable capacitor representing the capacitance change on the disc is coupled to an oscillator for generating a reference oscillation frequency. A pickup circuit for a video disc player, characterized in that the reference oscillation frequency is used as a carrier wave, frequency modulation is performed by capacitance changes on the disc, and the modulated wave is supplied to a resonant circuit to obtain an amplitude modulated output.