JPS647408B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video disc playback device equipped with a pick-up means that detects information recorded on a rotatable video disc as a change in capacitance, and particularly relates to a video disc playback device equipped with a pick-up means that detects information recorded on a rotatable video disc as a change in capacitance. Deterioration of the SN ratio due to dust etc. that adheres between the
It is an object of the present invention to provide a video disc playback device having a pick-up stylus pressure control function that can effectively prevent the problem without deteriorating the quality of playback signals (signals such as video, audio, tracking, etc.).

Conventionally, in capacitance detection type video disk playback devices, the disk is rotated while the pick-up needle is in contact with the surface of the disk, so minute dust gets between the disk and the pick-up stylus tip, and as a result, the pick-up needle There was a problem in that the output of the reproduced signal picked up at the end decreased and the S/N ratio deteriorated. It has been found that, as a means for preventing the deterioration of the reproduced signal due to the adhesion of dust, it is effective to increase the stylus pressure of the pick-up needle when dust adheres. In more recent research,
When dust begins to adhere, the amplitude of the reproduced output signal begins to decrease, and as the dust increases, the amplitude of the output signal decreases more rapidly. In this case, it has been found that if the pressure of the pick-up needle is slightly increased when the attached dust is small, the dust is removed and it becomes difficult for the dust to accumulate. Furthermore, in order to remove dust, it is effective to control the stylus pressure of the pick-up needle according to the amplitude of the reproduced signal. However, if the stylus force is simply controlled using a control voltage proportional to the amplitude of the reproduced signal, the stylus force will also change due to variations in the amplitude of the reproduced signal. In other words, variations in the level of the reproduced signal occur due to variations in the disc and the pickup needle, but even in this case, the stylus pressure will be different. In other words, it is effective to perform control so that a constant amount of change in stylus pressure is applied when the reproduced signal level changes at a constant rate, regardless of the magnitude of the replay signal level. To achieve this, the stylus force may be controlled using a control voltage proportional to the logarithm of the amplitude of the input signal.

On the other hand, since it is preferable that the reproduced signal output be at a constant level as much as possible, it is usually desirable to control the reproduced signal output to be constant using automatic gain control (AGC). In this case, if the above-mentioned stylus force control and AGC are provided independently, there is a problem that the circuit becomes complicated, and the system
There are problems such as an increase in the number of pins when converting to IC.

The present invention solves the above-mentioned problems, and is configured so that the AGC, which controls the playback signal output from the video disc at a constant level, and the stylus pressure control of the pick-up needle are controlled based on the same information. be. The present invention will be explained below based on illustrated embodiments.

FIG. 1 is a block diagram of main parts showing the principle of the present invention. In the figure, video disk 1 is connected to motor 3.
The change in capacitance caused by the pits, which are on the turntable 2 which is rotationally driven by the pick-up needle 5a at the tip of the pick-up means 5, is recorded (engraved) as information on the video disk 1.
The signal is picked up by the fly lead 7 and guided to the signal detector 8 . The signal detector 8 converts the capacitance change into an electrical signal and supplies a reproduced signal to the head amplifier 9.

A magnet 4 is attached to the pick-up means 5, and an electromagnet 6 for controlling needle pressure is arranged at a fixed portion near the magnet 4.
A coil is wound around the electromagnet 6, and the position of the magnet 4 is controlled according to the current flowing through the coil, and the pickup 5a for the video disc 1 is controlled.
The structure is such that the stylus pressure is controlled. The output of the head amplifier 9 is led to an output terminal 10 and supplied to a signal processing circuit (not shown). Here, the head amplifier 9 is a variable gain amplifier, and its gain is controlled by the voltage obtained by rectifying the signal at the output terminal 10 by the rectifier circuit 11, so that even if the input signal level from the signal detector 8 varies, The amplitude of the output signal obtained at the output terminal 10 becomes constant. That is, the head amplifier 9 and the rectifier circuit 11 constitute automatic gain control means. Here, the output of the rectifier circuit 11, that is, the gain control signal to the head amplifier 9, has a voltage corresponding to the amplitude of the signal reproduced from the video disc 1. In other words, when the input signal is large, the gain control voltage becomes large and the gain becomes low, and conversely, when the input signal is small, the gain control voltage becomes small and the gain becomes high, and in the end, the output signal obtained at the output terminal 10 remains at a constant level. controlled to maintain the

As mentioned above, the gain control voltage of the AGC corresponds to the level of the signal reproduced from the video disk 1, so this gain control voltage is supplied to the stylus pressure control system 12 including an amplifier etc. to control the electromagnet 6. By doing so, good stylus pressure control can be achieved. For example, if dust adheres between the video disc and the pick-up needle, the output will decrease and the gain control voltage will increase, so the electromagnet 6 is driven in accordance with the gain control voltage to increase the stylus pressure of the pick-up needle 5a.
It operates to remove dust, resulting in a stable playback signal output, and compared to the case of just AGC, it has the excellent effect of not causing any deterioration of the SN ratio.

FIG. 2 is a main part block diagram of an embodiment of the present invention, showing the configuration of the AGC and stylus pressure control system. In the figure, since the signal output from the signal detector 8 has a low level, it is amplified by a preamplifier 13 and applied to a variable gain amplifier 14. In the variable gain amplifier 14, the gain is controlled by the gain control voltage output from the index conversion circuit 18, and the amplitude of the output signal is made constant. This output signal then passes through the output amplifier 15, reaches the output terminal 10, and is supplied to a signal processing system (not shown). Further, a part of the output of the output amplifier 15 is supplied to the rectifier circuit 11.
The signal is added to the signal, is converted into a direct current according to the signal amplitude, and is supplied to the error amplifier 17. The error amplifier 17 is supplied with a reference voltage from the reference voltage source 16, and obtains a difference voltage between the DC component and the DC component corresponding to the amplitude of the previous output signal, that is, a DC voltage corresponding to an error with respect to a predetermined reference amplitude. This error voltage is applied to the index conversion circuit 18 to obtain a gain control voltage proportional to the index of the error signal.

Here, the input signal to the variable gain amplifier 14 is
V _i , the output signal is V _p , the gain control voltage to the variable gain amplifier 14 is V _c , and the error output of the error amplifier 17 is
When V _e and the gain are G, the following relationship holds: V _p = GV ...... (1) V _c = k ₁ e ^a2Ve ...... (2) where a: constant, k ₁ : constant Above (1) ), G = V _p /V _i , and the output signal V _p
is controlled to a constant level by AGC, so G∝ ₁ /V _i ...(3).

The gain of the variable gain amplifier 14 is set to the gain control voltage V _c
If it is linearly controlled by , then the following equation is obtained.

G=k ₂ V _c =k ₁ k ₂ e ^aVe ...(4) However, k ₂ : constant From equations (3) and (4), the following equation is obtained.

V _e ∝−logV _i (5) In short, the error signal obtained from the error amplifier 17 is proportional to the logarithm of the input signal _Vi . As mentioned earlier, increasing the stylus pressure in proportion to the logarithm of the input signal drop is effective in eliminating the effects of dust that has adhered between the video disc and the pick-up stylus tip. be. Therefore, the error output V _e which is the output of the error amplifier 17 is passed through the low-pass filter 19 to set a time constant, and then supplied to the needle pressure coil drive amplifier 20 to drive the pick-up needle 5.
A groove is formed to control the stylus pressure of a.

With this configuration, a constant level signal output by the AGC and a stable output signal that is free from the influence of dust due to the stylus pressure control can be obtained from the output terminal 10, and the reproduced image quality and sound quality of the video disc are improved. Furthermore, since the control signal (voltage) generator can be used commonly for AGC and stylus force control, the circuit configuration is not only simplified, but also has the effect of reducing the number of pins when implementing an IC.

FIG. 3 is a diagram showing a specific circuit configuration diagram of a variable gain amplifier and an index conversion circuit used in the present invention. In the figure, a signal obtained from a signal detector 8 is supplied to an input terminal 21, and is applied to the bases of transistors 35 and 37 through a capacitor 24. The bases of the transistors 34 and 36 are biased by a voltage source 27 through a resistor 26, and similarly the resistor 25 is connected to the bases of the transistors 35 and 36.
A bias of 37 is given. Resistors 38 and 39 are load resistances, and the output is obtained as a balanced output from between the output terminals 22 and 22'. Transistor 31,3
2, 34, 35, 36 and 37 are commonly used double balanced modulation circuits, and the signal applied to the input terminal 21 is transmitted through the transistors 31 and 32.
The signal is amplified with a gain proportional to the difference between the base voltages of , and is output to the output terminals 22 and 22'. Here, 33
represents a constant current source, and resistors 29 and 30 are bias resistors that supply equal bias from voltage source 28 to the bases of transistors 31 and 32.
The transistor 40 is a transistor for index conversion, and its collector is connected to the base of the transistor 32, and the base is connected to a voltage source 45 through a resistor 41.
It is connected to the. The collector of the transistor 42 is connected to the base of the transistor 40, and a constant voltage is applied to the base from a voltage source 44. The emitter reaches the control terminal 23 via the resistor 43.

In the double-balanced modulation circuit, when the transistor 40 is in the OFF state, the base voltages of the transistors 31 and 32 are equal and the gain is zero, but when current flows through the transistor 40, the gain is zero.
The base bias of 2 becomes unbalanced and the gain increases. In this case, the gain is proportional to the collector current of transistor 40. The collector current of transistor 42 is proportional to the voltage applied to control terminal 23. Therefore, the base voltage of transistor 40 is approximately inversely proportional to the voltage applied to control terminal 23. With respect to the base voltage (base-emitter voltage) V _BE of the transistor 40, its collector current I _c is expressed by the following equation.

However, I _p : Reverse saturation current q : Electron charge k : Boltzmann's constant T : Absolute temperature Therefore, I _c is approximately proportional to the index of V _BE .
As a result, the gain of the double balanced modulation circuit changes in proportion to the index of the control voltage applied to the control terminal 23. With this configuration, the variable gain amplifier 14 and index conversion circuit 18 shown in FIG. 2 are realized.

As described in detail above, according to the present invention, when playing back a capacitance detection type video disc, automatic gain control is performed on the amplitude of the playback signal, and the gain control voltage is given an exponential characteristic. By also supplying the stylus pressure control system,
Since the stylus force can be controlled in proportion to the logarithm of the input amplitude change, effective stylus pressure can be maintained regardless of the video disc playback level, and dust that may accumulate between the video disc and the pick-up stylus can be controlled. It can effectively remove dust, etc., and is hardly affected by the adhesion of dust. Therefore, the SN ratio of the reproduced signal does not deteriorate, and high-quality video and audio signals can be reproduced. Furthermore, as already mentioned, the advantages include the fact that the circuit configuration is simplified and it is easy to integrate into an IC, and its industrial value is extremely large.

[Brief explanation of drawings]

FIG. 1 is a basic block diagram of the main parts of the present invention, FIG. 2 is a block diagram of the main parts showing an embodiment of the invention, and FIG. 3 is a wiring diagram showing a specific circuit example of the main parts. 1...Video disk, 4...Magnet, 5
...Pickup means, 5a...Pickup needle, 6...Electromagnet, 8...Signal detector, 9...
... head amplifier, 11 ... rectifier circuit, 12 ... stylus pressure control system, 14 ... variable gain amplifier, 16 ... reference voltage source, 17 ... error amplifier, 18 ... index conversion circuit, 19 ... low-pass filter , 20... Amplifier for driving the stylus force coil, 40... Transistor for index conversion.

Claims (1)

[Scope of Claims] 1 Pickup means for detecting information recorded on a video disk as a change in capacitance; stylus pressure control means for controlling the stylus pressure of a pickup stylus of the pickup means; automatic gain control means for controlling the amplitude of the reproduced signal to be constant and outputting it to the reproduction output terminal; 2. A video disk reproducing apparatus, wherein the gain of the pick-up needle is controlled based on the gain control signal, and the stylus pressure control means controls the stylus pressure of the pickup needle based on the gain control signal. 2 The gain control signal output to the stylus force control means is
2. The video disc reproducing apparatus according to claim 1, wherein the signal is proportional to the logarithm of the amplitude of the signal reproduced from the video disc. 3. The automatic gain control signal has a variable gain amplifier, the gain of which is controlled by a signal obtained by exponentially converting the rectified error signal, and the stylus pressure of the pick-up needle is controlled by the rectified error signal. A video disc reproducing apparatus according to claim 1 or 2, characterized in that the video disc reproducing apparatus is constructed as follows. 4 The variable gain amplifier is configured with a double-balanced modulation circuit, and the collector current of the transistor connected to its control input terminal changes exponentially with the base-emitter voltage to perform exponential conversion. A video disc playback device according to claim 3, characterized in that it is configured as follows.