JPH0775084B2 - Video disk playback device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video disc reproducing apparatus for detecting information recorded on a video disc as a change in capacitance,
In particular, it is provided with a device for keeping a constant difference between the resonance frequency of the resonance circuit including the detection unit and the oscillation frequency of the oscillator that excites the resonance circuit, and the frequency deviation due to the variation of the resonance frequency of the resonance circuit. Of the operating point corresponding to the oscillation frequency of the oscillation circuit on the gradient of the resonance circuit response curve, that is, the video disc reproducing apparatus is set to a desired frequency difference. To do.

2. Description of the Related Art In recent years, as a video disc reproducing apparatus as described above, an apparatus having a device for keeping a constant difference between a resonance frequency of a resonance circuit and an oscillation frequency of an oscillator for exciting the frequency of the resonance circuit has been put into practical use. ing. (For example, JP-A-58-1640
(Gazette No. 39) Hereinafter, an example of the above-described conventional video disc reproducing apparatus will be described with reference to the drawings.

FIG. 3 and FIG. 4 are a main part configuration diagram of a conventional video disc reproducing apparatus and a frequency response voltage curve diagram of a resonance circuit.

In FIG. 3, reference numeral 32 denotes a capacitance change detection unit including a needle for detecting information recorded on a recording medium, 31 has one end grounded and the other end connected to the capacitance change detection unit 32. A flat conductor forms a distributed constant resonance line of λ / 4, and when connected to the capacitance change detection unit 32, it resonates at the resonance frequency (f ₃ ). Reference numeral 50 is a detection circuit for diode-detecting the excitation voltage from the oscillator 33 which excites the resonance line resonating at f ₃ at the oscillation frequency (f ₅ ).

Reference numeral 51 denotes a resonance frequency variable circuit composed of a voltage variable capacitance element, which automatically adjusts the frequency deviation to a desired set value together with the control circuit 52. 49 is a preamplifier circuit.

The operation of the video disc reproducing apparatus configured as described above will be described below.

When the recorded information is reproduced, the resonance frequency f ₃ of the resonance circuit formed by the capacitance changing section 32 and the resonance line 31 fluctuates due to the change in the capacitance, so that the oscillator that excites the resonance circuit is generated. The injected voltage of 33 is transmitted to the output loop 35 in a state of being AM-modulated and detected by the diode 36 to be a reproduction output signal. Further, from the detection circuit 50, the average voltage of the detected reproduction output, that is, the voltage (V _S ) corresponding to the oscillation frequency (f ₅ ) on the resonance circuit response voltage curve C forming the f ₃ is obtained, and the control is performed. In circuit 52, it is compared with the voltage of reference voltage source 47 (V _r2 ). In FIG. 4, since the V _S is smaller than the V _r2 , the reproduction output and the S / N ratio are lowered. Therefore, by applying the output voltage of the control circuit 52 to the voltage variable capacitance element 42 of the resonance frequency variable circuit 51 and setting the resonance frequency (f ₄ ) of the resonance frequency variable circuit 51 to f ₄₁ , the resonance line Since the resonance frequency variable circuit 51 is electromagnetically coupled to 31, the resonance frequency f _{3 of the} resonance circuit included in the resonance line 31 increases to f ₃₁ , and the resonance circuit response voltage curve changes from the curve C to the curve D. changes, V _S is equal to V _r2, reproduction output and S / N ratio is optimal.

INVENTION Problems to be Solved point However, in the structure described above, the resonance frequency f ₄ of the resonance frequency varying circuit 51, as in f _41, by approximating the resonance frequency f ₃ of the resonant circuit, the f _{As 3} is increased to f ₃₁ , the resonance line 31 and the resonance frequency variable circuit 51 are electromagnetically coupled, so that the voltage (V _m ) corresponding to the resonance frequency f ₃ on the resonance circuit response voltage curve C resonates. It decreases like the voltage (V _m1 ) corresponding to the resonance frequency f ₃₁ on the circuit response voltage curve D. Therefore, the reproduction output and the S / N ratio decrease. Further, the resonance frequency variable circuit 51 has a problem that the variable range of the resonance frequency f ₃ is narrow and the variation of the electrostatic capacitance detection unit cannot be suppressed.

In view of the above problems, the well by raising the resonance frequency f _3, is not changed voltage V _m corresponding to the resonance frequency f ₃ of the resonant circuit response voltage curve, i.e., the reproduction output and S / N without ratio decreases, in which the variable range of the resonance frequency f ₃ to provide a wide video disk reproducing apparatus.

Means for Solving the Problems In order to solve the above-mentioned problems, a video disk reproducing apparatus of the present invention has a capacitance change detecting section at an open end of a resonance line including an inductance circuit element whose one end is grounded. , A voltage variable capacitance element is connected in the middle of the resonance line, and a part of the inductive circuit element is shared to form an automatic frequency control loop, and a variable frequency resonance circuit is provided.

Operation The present invention constitutes the automatic frequency control loop without the reproduction output and the S / N ratio being reduced by the above-mentioned configuration.

Embodiment A video disc reproducing apparatus according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an essential part of an embodiment of the present invention, FIG. 2 is a frequency response voltage curve diagram of a resonance circuit of the present invention, and 2 is a needle for detecting information recorded on a recording medium. The capacitance change detection unit 1 includes a flat conductor having one end grounded and the other end connected to the detection unit 2 and arranged on an insulating substrate, and constitutes a λ / 4 distributed constant resonance line. Therefore, by connecting to the capacitance change detection unit 2, it resonates at the resonance frequency (f ₀ ). Reference numeral 4 denotes an input loop (inductance that is electromagnetically coupled to the resonance line 1 for injecting the output of the oscillator 3 for exciting the resonance line 1 resonating at f ₀ at the oscillation frequency (f ₁ ) into the resonance line 1. 5 is an output loop (inductivity circuit element) electromagnetically coupled to the resonance line 1 in order to absorb the excitation voltage from the oscillator 3 that excites the resonance line 1 resonating at f _0. Yes, 6 is a diode for detecting the induced electromotive force generated in the output loop 5, and 7 and 8 are capacitors and resistors which are rectification load circuits of the diode 6.

When the recorded information is reproduced, the f ₀ changes in accordance with the capacitance change of the capacitance change detection unit 2, and the injected voltage from the resonance circuit exciting oscillator 3 of the f ₀ is electromagnetically coupled to the resonance line. Therefore, the injected voltage is injected by the input loop 4, and the injected voltage is transmitted to the output loop 5 electromagnetically coupled to the resonant line 1 in a state of being AM-modulated. The AM modulated recording signal transmitted to the output loop 5 is detected by the diode 6 and is used as a reproduction output. 15 is the average voltage of the detection reproduction output signal from the diode 6, that is,
It is a resistor for detecting the voltage (V _D ) corresponding to the oscillation frequency (f ₁ ) on the resonance circuit response voltage curve A that constitutes the above f ₀ . The resonance frequency of the resonance circuit formed by the output loop 5 and the diode 6 is (f ₂ ). Reference _numeral 12 is a DC voltage comparator for making a decision with respect to the V _D and the voltage V _r1 of the reference voltage source 13 and constitutes a control circuit 21. The output voltage of the control circuit 21 is applied to the voltage variable capacitance element 9,
An automatic frequency control (AFT) loop is configured with the capacitor 10 and a part of the resonant line 1 (inductance circuit element) (on the side of the voltage variable capacitance element connection point to the ground point).

That is, in FIG. 2, it is assumed that the frequency response voltage curve of the resonance circuit is set as a curve A due to the variation of the capacitance change detection unit 2. At this time, the voltage V _D corresponding to the above f ₁
Is smaller than V _r1 , the reproduction output and S / N ratio are lowered. In order to solve the above condition, the voltage applied to the voltage variable capacitance element 9 of the AFT loop is increased and the capacitance of the AFT loop is reduced, so that the resonance frequency f _{0 of the} resonance circuit included in the resonance line 1 becomes Increasing to f ₀₁ , the resonance circuit response voltage curve changes from curve A to curve B, making the voltage V _D corresponding to the resonance frequency f ₁ equal to V _r1 . As a result, the reproduction output and the S / N ratio are set to the optimum values.

As described above, according to this embodiment, the capacitance change detector 2 is connected to the open end of the resonance line 1 including the inductance circuit element whose one end is grounded, and the voltage change is performed in the middle of the resonance line 1. By connecting the capacitive element 9 and sharing a part of the inductive circuit element to provide a variable frequency resonance circuit forming an AFT loop, the resonance frequency f ₀ on the resonance circuit response voltage curve can be dealt with. Voltage (V _P )
Has almost no variation with the change of f ₀ , that is, the gradient around the f ₁ does not vary with the variation of f ₀ , so that the signal detection sensitivity becomes constant. Therefore, the signal detection sensitivity can be kept constant with the adjustment of the resonance frequency f ₀ .

In the video disc reproducing apparatus which we have trial, when constructed in accordance with the prior art, in order resonance frequency varying circuit 51 is electromagnetically coupled to the resonant line 31, the variable range 40MH _Z (Min 980MH _Z of the resonance frequency f ₃ , voltage V _m corresponding to the resonance frequency f ₃ of the resonant circuit response voltage curve at that time up to 1020MH _Z)
Was reduced by 35%. On the other hand, in the case of the configuration according to the present embodiment, since the resonance frequency variable circuit 20 shares a part of the resonance line 1 to form the AFT loop, the resonance frequency f
₀ of the variable range of 100 MHz _Z (Min 970MH _Z, maximum 1070MH _Z) and expanded, the resonance frequency f ₀ of the resonant circuit response voltage curve at that time
The voltage V _P corresponding to fluctuates only by 20%. Further, 40MH _Z (Min 980MH _Z within the variable range of the same resonant frequency as the conventional example,
In maximum 1020MH _Z), the voltage V _P only a change of 10%.

As described above, the present invention has a distributed constant type of λ / 4 configured to connect the capacitance change detection unit to the open end of the resonance line including the inductance circuit element whose one end is grounded. Frequency resonance variable second resonance circuit in which an automatic frequency control loop is configured by connecting a voltage variable capacitance element in the middle of the resonance line and sharing a part of the inductance circuit element By providing the circuit, the variable range of the resonance frequency of the first resonance circuit can be expanded without lowering the reproduction output and the S / N ratio. Therefore, it is possible to cover a wide range of variations in the capacitance detection unit,
Reproduction output and S / N ratio hardly decrease.

[Brief description of drawings]

FIG. 1 is a schematic view of the essential parts of an embodiment of the present invention, and FIG.
FIG. 3 is a graph showing a frequency response voltage curve of a resonance circuit according to an embodiment of the present invention, FIG. 3 and FIG. 4 are main block diagrams of a conventional video disk reproducing apparatus and a frequency response voltage curve of the resonance circuit. It is a graph. 1 ... λ / 4 distributed constant type resonance line, 2 ... Capacitance change detection part, 3 ... Oscillation circuit, 4 ... Input loop, 5 ... Output loop, 19 ... Detection circuit, 20 ... Resonant frequency variable circuit, 21 ... Control circuit.

Claims (1)

[Claims] 1. A detection unit for detecting information recorded on a video disk as a change in electrostatic capacity, a resonance circuit and an oscillator for exciting the resonance circuit, and one end of the resonance circuit is grounded. A distributed constant type first resonance circuit of λ / 4, which has a resonance line including a first inductance circuit element and is configured to connect the detection unit to an open end of the resonance line, A voltage variable capacitance element is connected in the middle of the resonance line, a part of the first inductance circuit element is shared, and a frequency variable second resonance circuit that constitutes an automatic frequency control loop is provided. Characteristic video disk player.