JPS58128036A - Static capacitance type reproducer - Google Patents

Abstract

PURPOSE:To keep the output of an oscillator for capacitance detection constant, by providing a control means for detecting the output voltage of the oscillator and controlling the output voltage of the oscillator to the direction close to a prescribed value in reponse to the output. CONSTITUTION:In a Figure, 14 is an oscillation output detection circuit, comprising an AM detection circuit consisting of a diode, resistors and capacitors, where the output of an oscillator 6' applied to an input terminal 18 is AM-detected and a DC voltage in response to the oscillator output voltage is outputted to an output terminal 19. 20 is a comparator, to the noninverting input (+) of which a reference voltage 21 is connected and to the inverting input (-) of which the output 19 is connected, and the comparison output is connected to a voltage supply terminal 12 of the oscillator 6'. Thus, when the output voltage of the circuit 14 is lower than the reference voltage 21, the output of the comparator 20 increases the output of the oscillator 6' and when the output voltage of the circuit 14 is higher than the reference voltage 21, the output of the oscillator 6' is decreased, allowing to make the output of the circuit 14 constant, resulting in that the output of the oscillator 6' is made constant.

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 maintain a constant output voltage of an IH generator for capacitance detection.

Conventionally, a capacitance detection type video disc playback device outputs an output by detecting a change in capacitance between a recording medium and a pickup needle. , the change in capacitance as shown in Figure 1 is a combination of 1 MIgljil! constructed with a fixed inductive element connected to the pick-up needle! This resonant circuit is inductively coupled to an excitation circuit connected to an oscillator with a constant frequency. The above encouragement J [! The output of the oscillator applied to the 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, it undergoes amplitude modulation as the resonant frequency changes due to the information on the disk, and the output of this output circuit is amplitude demodulated. By doing this, information signals on the disk are extracted. Further, the amplitude demodulation circuit connected to the output circuit uses a single wave detection circuit or a voltage doubler rectifier circuit configured using diodes, and the oscillation frequency is selected to be about 9181M1z.

Figure 1 is a configuration diagram of a basic conventional capacitive playback device, in which (1) shows the capacitance that changes depending on the mechanical information between the pick-up needle and the disk, (2) shows the capacitance detection device, and ( 3
) is a conductive circuit element that forms a resonant circuit [) together with the capacitor (1); (IS) is an excitation circuit connected to the output side of the oscillator (6) and supplies energy to the resonant circuit (4); (7) is an output circuit that takes out a signal amplitude-modulated by information on the disk by inductive coupling, (8) is a diode that detects 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 needs to be maintained at a constant value for the following reasons.

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

(2) When the oscillation output is large, unnecessary radiation increases.

Furthermore, since the frequency used is as high as 915 MHz, there are many variations in the oscillation output due to variations in transistors and other circuit elements, and an oscillation output adjustment process is required during mass production. Furthermore, since changes due to aging, temperature changes, and power supply voltage fluctuations of the oscillation transistor cannot be absorbed, 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 that is connected to the output of an oscillator and a resonant circuit that is constituted by a constant inductive circuit element regardless of the open capacitance between the recording medium and the two-wave circuit and the information signal recorded on the recording medium. An excitation circuit that supplies energy to the resonant circuit; and an output circuit that extracts an amplitude modulation component from the resonant circuit and performs amplitude detection to detect the information signal; and output voltage detection that detects the output voltage of the oscillator. By providing a control means for controlling the oscillator output voltage in a direction approaching a predetermined voltage value in accordance with the output of the output voltage detector, the output voltage of the oscillator can be stabilized and initial variations can be reduced. , which achieves good reproduction without deterioration of reproduced image quality or increase in unnecessary radiation due to aging of the element or temperature change.One embodiment of the present invention will be described below based on FIGS. 2 to 4. explain.

In Fig. 2, 6' is an oscillator corresponding to the oscillator (6) in Fig. 1, and its specific circuit, as shown in Fig. 4, includes an oscillation transistor (g) and a resonant circuit section that determines the oscillation frequency. It consists of a control voltage supply terminal, - is an oscillator output terminal, etc. In Fig. 2, (B) is an oscillation output detection circuit, and as shown in Fig. 8, a diode - and a resistor are used. It consists of an AM detection circuit 1 consisting of a shaft and a capacitor, and performs AM detection on the output of the oscillator (6/) applied to the input terminal (2) and outputs a DC voltage corresponding to the oscillator (6/ hearing voltage) to the output terminal ( 2) is a comparator whose non-inverting input (g) is connected to the reference voltage - and whose inverting input terminal θ is connected to the output terminal (to). Connected to supply terminal So.

Because of this configuration, when the output voltage of the oscillation output detection circuit (b) is much lower than the reference voltage, the comparator section output acts to increase the oscillator (6/me output), and the oscillation output detection circuit When the output voltage of - is higher than the reference voltage -, it acts to reduce the oscillator (6' specific force), so the output of the oscillation output detection circuit (b) becomes constant, and as a result, the output of the oscillator (61) becomes constant.

Furthermore, by using a diode similar to diode (1) as the diode μs of the oscillation output detection circuit, the operating points can be set to be the same, and the following effects can be obtained.

That is, when the characteristics of the AM detection circuit composed of diode J deteriorate due to temperature changes, the information signal output generated at the output terminal (9) becomes smaller, but at that time, the output of the oscillation output detection circuit also becomes smaller. Therefore, in this case, the oscillator (6') output is controlled to be high, and the information signal output generated at the output terminal (9) can be prevented from becoming small. 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.

・Initial variations in oscillation transistors and other circuit elements ・Output changes due to aging of the above elements O Characteristic changes due to temperature and humidity ・Output changes due to power supply voltage fluctuations, so there is no deterioration in playback image quality or increase in unnecessary radiation. This makes it possible to achieve good playback.

[Brief explanation of the drawing]

Figure 1 is a basic configuration diagram of a signal detection section of a conventional capacitive reproducing device, Figure 2 is a configuration diagram of essential parts showing an embodiment of the present invention, and Figures 8 and 4 are Figure 2. FIG. (1)...Capacitance between the recording medium and the pickup, (2)...Capacitance detection device, (Gradient...Inductive circuit element, (4)...Resonant circuit, ( Season: Excitation circuit,
(6')...Oscillator, (7)--Output circuit, (8)
(2)...Diode, (B)...Oscillation output detection circuit, So...Comparator, 4-...Reference voltage agent Yoshihiro Morimoto Figure 1 Figure j

Claims (1)

[Claims] 1. A resonant circuit constituted by a constant inductive circuit element regardless of the electrostatic capacitance between a recording medium and a pickup needle and an information signal recorded on the recording medium, and an oscillator. An excitation circuit that is connected to an output side and supplies energy to the resonant circuit, and an output circuit that extracts an amplitude modulation component from the resonant circuit, performs amplitude detection, and detects the information signal, and detects the output voltage of the oscillator. A capacitance type reproducing device comprising: an output voltage detector; and a control means for controlling the output voltage of the oscillator in a direction approaching a predetermined voltage value in accordance with the output of the output voltage detector. 2. The capacitive reproducing device according to claim 1, wherein the output voltage detector is configured to use a dimeade having the same characteristics as the amplitude detection diode in the output circuit to perform amplitude detection of the output voltage of the oscillator. 8. 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.