JPS60197963A - Pickup circuit of video disk player - Google Patents

Abstract

PURPOSE:To obtain a normal reproducing function which is not influenced by the external disturbance by connecting a frequency variable resonance circuit and a constant frequency resonance circuit having a capacity which is varied in accordance with a recording signal, to a reference oscillator through an isolator, and detecting amplitude modulating outputs of each resonance circuit as signals having the opposite polarity to each other. CONSTITUTION:A capacity 1 of a resonance circuit 3 is varied by receiving an oscillating power of a frequency f0 from a reference oscillating circuit 4, and in accordance with a signal recorded in a disk from the circuit 3, a carrier wave of a frequency f0 is brought to an amplitude modulation and outputted from the circuit 3, picked up by a pickup coil 6, and a demodulating signal is outputted through a detecting circuit 10 and a pre-amplifying circuit 11. On the other hand, when a disturbing wave of a frequency f1 being near f0 is inputted, a beat of a frequency f=f0-f1 is picked up by the pickup 6 and a pickup 16 to a constant frequency resonance circuit 14, and detected as two signals of an opposite phase by a detecting circuit 10 and 20 having a detecting diode 7 or 17 of a forward connection or a reverse connection, and they are negative each other.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a pickup circuit for a video disc player that picks up a signal recorded as a capacitance change on a video disc.

<Prior Art> An example of this type of pickup circuit is the one shown in FIG. The pickup circuit of this video disk player includes a variable frequency resonant circuit 3 formed between a disk (not shown) and an electrode of a pickup needle, and consisting of a variable capacitor 1 and a tuning coil 2, which are changed as a recording signal.

A reference frequency oscillation circuit 4 is coupled to this resonant circuit 3 via a coupling coil 5 . The oscillation frequency fo of the reference oscillation circuit 4 is set at an appropriate position on the slope of the resonant frequency characteristic waveform of the resonant circuit 3 shown in FIG. The pickup circuit of this video disc player also includes a pickup coil 6 for picking up the amplitude modulated output of the resonance circuit 3, and a detection circuit 10 connected to the pickup 6. This detection circuit 10 includes a detection diode 7, a resistor 8, and a capacitor 9h connected in the forward direction. Furthermore, a preamplifier circuit 11 for amplifying the output of the detection circuit () is provided as required.

In the conventional device configured in this way, the reference oscillation circuit 4
The variable capacitor 1 of the resonant circuit 3, which receives the oscillation power of the frequency fO from the tIS2, is changed as the disk rotates, and the resonant frequency of the resonant circuit 3 is shifted from the solid line to the broken line in the tIS2 diagram. According to the signal pre-recorded on the disk in this way, as shown in FIG. 3 (8), the carrier wave of frequency fO is amplitude-modulated and output from the resonant circuit 3, and is picked up by the pickup coil 6. . This amplitude modulated signal is demodulated by the detection circuit IO, amplified by the preamplifier circuit 11, and output as a demodulated signal as shown in FIG. 3 (L,). This demodulated signal naturally corresponds to the signal recorded on the disc.

However, in the pickup circuit of such a conventional video disc player, when a high-energy interference wave with a frequency f1 close to the frequency fO of the reference oscillation circuit 4 enters from the outside and is not connected to the reference frequency fO. and frequency f=f
Beats o to 11 occur, and unnecessary components other than the signals originally recorded on the disk are included in the demodulated signal and output. These unnecessary components not only cause striped disturbances on the screen and noise in the audio, but also may cause tracking disturbances when they coincide with the tracking signals recorded on the disk.

Purpose The present invention has been made in view of the above, and an object of the present invention is to provide a pickup circuit for a video disc player that is not affected by external disturbances and can perform normal playback functions.

<Examples> The present invention will be described in detail below based on illustrated examples.

FIG. 4 is a circuit diagram of a pickup circuit of a video disc player according to an embodiment of the present invention, and in the figure, ff11
Components having functions corresponding to those shown in the figure are given the same names and symbols as in FIG. 1.

That is, a variable frequency resonant circuit 3 is formed between a disk (not shown) and an electrode of a pickup needle, and is made up of a variable capacitor 1 and a tuning coil 2, which is changed as a recording signal.
Equipped with This resonant circuit 3 includes a reference frequency oscillation circuit 4
are coupled via coupling coil 5. The oscillation frequency 10 of the reference oscillation circuit 4 is set at an appropriate position on the slope of the resonant frequency characteristic waveform of the resonant circuit 3 shown in FIG. The pickup circuit of this video disc player includes a pickup coil 6 for picking up the amplitude modulated output of the resonant circuit 3, and a detection circuit 10 connected to the pickup 6. The detection circuit 10 includes a detection diode 7, a resistor 8, and a capacitor 9 connected in the forward direction. Furthermore, a preamplifier circuit 11 is provided to amplify the output of the detection circuit 10 as necessary.

Reference numeral 14 denotes a frequency-fixed resonant circuit consisting of a fixed capacitor 2 and a tuning coil 13, and a reference frequency oscillation circuit 4 is coupled to this resonant circuit 14 via a coupling coil 15. As shown in FIG. 5, the resonant frequency wave characteristics of the resonant circuit 14 are such that the oscillation frequency ro of the reference oscillation circuit 4 is located at an appropriate position on the slope of the resonant frequency characteristic waveform. Set. In addition, the pickup circuit of this video disc player includes a pickup coil 16 for picking up the constant amplitude output of the frequency-fixed resonance circuit 14, and a detection circuit 2 connected to the pickup 6.
0. The detection circuit 20 includes a detection diode 17, a resistor 18, and a capacitor 19 connected in opposite directions. This detection circuit 20 is commonly connected to the preamplifier circuit 11 and another detection circuit 10 . Furthermore, isolators 21 and 22 are inserted between each of the coupling coils 5 and 15 and the reference oscillation circuit 4, respectively.

According to the pickup circuit of the video disc player configured in this way, the frequency to
The variable capacitance 1 of the resonant circuit 3 receiving the oscillation power is changed as the disk rotates, and the resonant frequency of the resonant circuit 3 is shifted from the solid line to the broken line in FIG. 2. According to the signal previously recorded on the disk in this way, the carrier wave of frequency fo is amplitude-modulated and output from the resonant circuit 3, as shown in FIG. 3 (8), and is picked up by the pickup coil 6. Ru. This amplitude modulated signal is demodulated by the detection circuit 10 and amplified by the preamplifier circuit 11, and is shown in FIG.
This is the same as the conventional method in that a demodulated signal as shown in b) is output.

However, the frequency 1 close to the frequency fO of the reference oscillation circuit 4
The frequency f=1θ~[1
The beat is picked up by the pickup 6 and also picked up by the pickup coil 16, and is detected by the detection circuit 10 having the forward-connected detection diode 7 and the detection circuit 20 having the reverse-connected detection diode 17, as shown in FIG. , ), they are detected as two signals with the same frequency and opposite phases. When the beat signals detected as two signals with the same frequency and opposite phases are simultaneously input to the preamplifier circuit 11, they neutralize each other, resulting in the result shown in Fig. 6 (1)). As shown, the beat will be deleted.

Furthermore, if the two resonant circuits 3 and 14 are directly coupled to the reference oscillation circuit 4, the change in the pits of the disk will cause the resonant circuit to
When the frequency of the reference oscillation circuit 4 changes, the frequency of the reference oscillation circuit 4 is changed, albeit slightly. When this frequency fluctuation of the reference oscillation circuit 4 is transmitted to another resonant circuit 14, this fluctuation is detected with the opposite polarity, canceling the output of the detection circuit 10 within that range, and the CN ratio (ratio ) occurs. However, since the isolators 21 and 22 are interposed between the reference oscillation circuit 4 and the resonant circuits 3 and 14, the influence of fluctuations in the resonant frequency does not affect the reference frequency 11, and the fidelity of the signal is maintained. This ensures good reproduction and a high CN ratio.

Effects> As described above, the present invention provides a variable frequency resonant circuit having a capacitance that can be changed in accordance with a recording signal.

and a constant frequency resonant circuit, and connect these two resonant circuits to a reference oscillation circuit via an isolator, respectively.
Each detection circuit is connected to each pickup coil that picks up the amplitude modulation output from each resonant circuit, the polarity of the detection diode of each detection circuit is reversed, and the output end of each detection circuit is commonly connected to a common output point. Therefore, external disturbances can be detected by two detection circuits as signals with opposite polarities and the same frequency, and these can be mutually neutralized and erased. Also, a frequency variable circuit that has a capacity that can be changed in accordance with the recorded signal can be used. Since the frequency fluctuation of the resonant circuit is prevented from affecting the frequency of the reference oscillation circuit by the isolator, faithful signal reproduction and a high CN ratio can be obtained.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of the conventional example, Figure 2 is a frequency characteristic diagram of its resonant circuit, Figure 3 (8) is a waveform diagram of its amplitude modulation output, and Figure 3 (b) is the waveform of its demodulated wave. 4 is a circuit diagram of a pickup circuit of a video disc player according to an embodiment of the present invention, FIG. 5 is a frequency characteristic diagram of its constant frequency resonant circuit, and tj & 6 (a) is a diagram of two detection circuits. The waveform diagram of the demodulated wave, FIG. 6(b), is a waveform diagram of the combined output of both transverse wave circuits. 1... Capacity, 3... Frequency variable resonant circuit, 4...
Reference oscillation circuit, 6...Pickup coil, 7...
Detection diode, 10...Detection circuit, 14...Constant frequency resonance circuit, 16...Pickup coil, 17.
...Detection diode, 21.22...Isolator. Applicant Sharp Corporation Agent Patent Attorney Oka 1) Hide Kazu

Claims (1)

[Claims] (1) A pickup circuit for a video disc player that picks up a signal recorded as a 4-bit variable capacitance on a video disc uses a variable frequency resonant circuit and a constant frequency resonant circuit, each having a capacitance that can be changed in accordance with the recorded signal. These two resonant circuits are each connected to a reference oscillation circuit via an isolator, each detection circuit is connected to each pickup coil that picks up the amplitude modulated output from each resonant circuit, and the polarity of the detection diode of each detection circuit is set. A pickup for a video disc player in which the output ends of each detection circuit are connected to each other in opposite directions.