JPS6235172B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capacitive reproducing device that detects an information signal recorded on a recording medium as a change in capacitance between the recording medium and a detection section, and has an object thereof. The purpose of this invention is to provide a device that can keep the output voltage of an oscillator constant for capacitance detection.

Conventionally, a capacitance detection type video disc playback device extracts an output by detecting a change in capacitance between a recording medium and a pickup needle. This change in capacitance changes the resonant frequency of a resonant circuit constructed with a fixed inductive element connected to the pickup needle. This resonant circuit is inductively coupled to an excitation circuit connected to a constant frequency oscillator. The output of the oscillator applied to the excitation circuit undergoes amplitude modulation by the resonant circuit, and is further output through an output circuit coupled to the resonant circuit by inductive coupling. Since the oscillation frequency of the oscillator is selected to be different from the resonant frequency of the resonant circuit, the resonant frequency undergoes amplitude modulation as the information on the disk changes, and the output of this output circuit is amplitude demodulated. information signals on the disk are extracted. Furthermore, the amplitude demodulation circuit connected to the output circuit uses a single wave detection circuit or a voltage doubler rectifier circuit constructed using diodes, and the oscillation frequency is selected to be approximately 915MHz.

FIG. 1 is a configuration diagram of a basic conventional capacitive playback device, in which 1 is a capacitance that changes depending on mechanical information between the pick-up needle and the disk, 2 is a capacitance detection device, and 3 is the capacitance 1. An inductive circuit element 5 is connected to the output side of an oscillator 6 to suppress energy to the resonant circuit 4, and 7 is an inductive circuit element that induces a signal whose amplitude has been modulated by information on the disk. An output circuit is taken out by coupling, 8 is a diode for detecting the amplitude of the output of the output circuit 7, and 9 is an output terminal.

Conventionally, the oscillator 6 of a video disk reproducing apparatus of this type is usually constituted by a transistor, and its oscillation output must be maintained at a constant value for the following reasons.

(1) If the oscillation output is small, sufficient detection voltage cannot be obtained, and the S/N of the reproduced signal deteriorates.

(2) If the oscillation output is large, unnecessary radiation will be large.

Also, since the frequency used is 915MHz,
There are many variations in oscillation output due to variations in transistors and other rotating elements, and an oscillation output adjustment process is required during mass production. Furthermore, since it is not possible to absorb changes due to aging, temperature changes, and power supply voltage fluctuations in the oscillation transistor, there are drawbacks such as deterioration of reproduced image quality and increase of unnecessary radiation depending on usage conditions.

Therefore, the present invention provides a resonant circuit constituted by a constant inductive circuit element regardless of the electrostatic capacitance between a recording medium and a pickup and an information signal recorded on the recording medium, and a resonant circuit that is connected to the output of an oscillator. an excitation circuit that supplies energy to a resonant circuit; an output circuit that extracts an amplitude modulation component from the resonant circuit and performs amplitude detection with a first diode to detect the information signal;
an output voltage detector that performs amplitude detection using a diode, and a control means that controls the oscillator output voltage in a direction approaching a predetermined voltage value in accordance with the output of the output voltage detector, and the first and second diodes. By making the same characteristics and setting the same operating point, the oscillator output voltage is stabilized, resulting in less initial variation, no deterioration of playback quality due to element aging or temperature changes, and no increase in radiation. One embodiment of the present invention will be described below with reference to FIGS. 2 to 4.

In FIG. 2, 6' is an oscillator corresponding to the oscillator 6 in FIG. 1, and its specific circuit, as shown in FIG. 4, is composed of an oscillation transistor 10, a resonance circuit 11 that determines the oscillation frequency, etc. There is. Note that 12 is a control voltage supply terminal, and 13 is an oscillator output terminal. Further, in FIG. 2, 14 is an output voltage detector, which is composed of an AM detection circuit consisting of a diode 15, a resistor 16, and a capacitor 17 as shown in FIG. AM detection is performed and a DC voltage corresponding to the 6' output voltage is output to the output terminal 19. 20 is a comparator whose non-inverting input (+) is connected to a reference voltage 21 and whose inverting input terminal (-) is connected to the output terminal 19, and the comparison output is connected to the voltage supply terminal 1 of the oscillator 6'.
Connected to 2.

With this configuration, the output voltage detector 14
When the output voltage of the output voltage detector 14 is lower than the reference voltage 21, the comparator 20 output acts to increase the output of the oscillator 6', and vice versa when the output voltage of the output voltage detector 14 is higher than the reference voltage 21. Since it acts to reduce the output of the oscillator 6', the output of the oscillation output detection circuit 14 becomes constant, and as a result, the output of the oscillator 6' becomes constant.

Furthermore, since the diode 15 of the output voltage detector 14 is the same as the diode 8 and the operating points are set to be the same, the following effects can be obtained.

That is, when the characteristics of the AM detection circuit composed of the diode 8 deteriorate due to temperature changes, the information signal output generated at the output terminal 9 becomes smaller;
At that time, the output of the output voltage detector 14 also becomes small, so in this case, control is performed to increase the output of the oscillator 6', and it is possible to prevent the information signal output generated at the output terminal 9 from becoming small. , the information signal output can be temperature compensated.

As described above, according to the capacitive reproducing device of the present invention, the control loop operates so that the output voltage of the oscillator is constant, so that it is possible to avoid the following fluctuation factors.

Γ Initial variations in oscillation transistors and other circuit elements Γ Output changes due to aging of the above elements Γ Characteristic changes due to temperature and humidity Γ Output changes due to power supply voltage fluctuations In addition, the first diode and the second diode have the same characteristics. Since the device operates at the same operating point, the configuration can be simplified, sufficient temperature compensation can be performed, and a drop in information signal output can be prevented. Therefore, it is possible to realize good reproduction without deterioration in reproduction image quality or increase in unnecessary radiation.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of a signal detection section of a conventional capacitive reproducing device, FIG. 2 is a configuration diagram of main parts showing an embodiment of the present invention, and FIGS. It is a main part specific circuit diagram. 1... Capacitance between recording medium and pickup, 2... Capacitance detection device, 3... Inductive circuit element, 4... Resonant circuit, 5... Excitation circuit, 6'...
... Oscillator, 7 ... Output circuit, 8 ... Diode [first diode], 14 ... Output voltage detector,
15...Diode [second diode], 20
... Comparator, 21 ... Reference voltage.

Claims (1)

[Claims] 1. A resonant circuit constituted by a constant inductive circuit element regardless of the capacitance between the recording medium and the pickup needle and the information signal recorded on the recording medium, and the output side of the oscillator. an excitation circuit that is connected to the oscillator and supplies energy to the resonant circuit; an output circuit that extracts an amplitude modulation component from the resonant circuit and performs amplitude detection with a first diode to detect the information signal; an output voltage detector that performs amplitude detection using a diode No. 2; and a control means that controls the output voltage of the oscillator in a direction approaching a predetermined voltage value in accordance with the output of the output voltage detector. A capacitive reproducing device in which the characteristics of the first diode and the characteristics of the second diode of the output circuit are set to be the same and the operating point is set to be the same. 2. The capacitive reproducing device according to claim 1, wherein the output voltage of the oscillator is controlled by changing the voltage supplied to the oscillator.