JPS60201789A - Reproducing circuit of video disk - Google Patents

Abstract

PURPOSE:To avoid malfunction of a rotation servo due to the occurence of noises by supressing a lower frequency component than a carrier frequency corresponding to a synchronizing signal of frequency-modulated high frequency signal, which is reproduced at the time of de-tracking. CONSTITUTION:A reproduction signal read out from a disk by means of a light head is supplied to an input terminal 37, and added to an amplifier 10. Gains of the amplifier 10 become larger and has a characteristic of a high-band compensation, when a transistor 35 is turned on and when a trap circuit of 4.5- 5MHz consisting of a resistance 18, a coil 29 and a capacitor 30 is held in a circuit arrangement. Since a control signal at a low level is added from a terminal 33 at the time of a normal reproduction, the transistor 35 is turned off, which keeps the trap circuit still in recess, and gains of the amplifier 10 become smaller. As a result, a reproduction signal of the light head is band-controlled through a suppressing trap circuit <=2MHz consisting of a BPF38, capacitors 21 and 23 and coils 22 and 24.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a reproducing circuit for a video disc on which a video signal is FM-modulated and recorded.

``Background Art and Problems Thereof'' A video disc playback device is known that plays back a video signal by irradiating a color video signal that is FM modulated and recorded as a geometric pattern of spiral tracks. The video signal for one frame is FM-modulated and recorded on one track.The white peak level of the modulated signal is, for example, 9.3 MHz, the pedestal level of the modulated signal is, for example, 8 MHz, and the modulated signal is FM-modulated and recorded. The sync frequency of the signal is FM modulated to, for example, 7.6 MHz.

On this video disc, an address is recorded for each field. This address is specified during a search operation in which the user searches for a desired image, and a reproduction synchronization signal is used to apply rotation servo to the spindle motor during this search operation. During this search operation, the optical head moves at a relatively high speed in the radial direction of the disk, and performs a reproducing operation across a plurality of tracks.

In conventional video disc playback devices, a malfunction may occur in the rotational servo of the spindle motor during this search operation, resulting in a problem that the image after the search operation is distorted. This occurs because noise that hangs below the sync level Sy occurs in the reproduced video signal, and this noise cannot be distinguished from the synchronization signal.

This sink has very low level noise.

As shown by N in the waveform shown in FIG. 2 which is obtained by demodulating the reproduction signal of the optical head during the search operation shown in FIG. 1, the time T when the optical head passes through an area where no track is formed.
, ! It occurs at T2 + T3 + 'r4 + 'r.

This noise N often occurs particularly in images in which color signals such as color par signals are saturated.

At times T1 to T5 when the optical head passes through an area where no track is formed, the reproduced output signal of the optical head attenuates, as shown in an enlarged view in FIG. When this attenuated reproduced output signal is further enlarged, as shown in Figure 4A, in the part of the image where there is no color signal, there is a signal with sufficient carrier components remaining, and the color signal is saturated. In the case of a color par signal, etc., there is almost no carrier component remaining, as shown in FIG. 4B. The reason for this is that the attenuation of the reproduced output signal from time T□ to T, when the optical head passes through an area where no tracks are formed, is not uniform at any frequency, and the higher the frequency, the more the attenuation is This is thought to be due to the large amount.

In other words, as shown in the spectrum diagram of FIG. 5A, the image of the part without one color signal has a frequency f
s and the pedestal level and the corresponding frequencies tl, fp
It consists of carrier and sideband components of the white peak level and the corresponding frequency/wave number fw.

As shown in the spectrum diagram of FIG. 5B, the image of the saturated portion of the color signal contains, in addition to the carrier and sideband components of the frequencies fs, fp, and fw mentioned above, an upper sideband of the frequency fcu of the color signal. Color signal frequency fcl
Includes lower sideband. During detracking when the optical head passes through an area where no track is formed, the higher the frequency, the greater the attenuation of the reproduced output signal. Assuming that, the frequency spectrum shown in FIG. 6A will be obtained. As is clear from FIG. 6A, the carrier component is preserved, albeit at a small level. On the other hand, the reproduced output signal in which the chrominance signal is saturated is the carrier of the luminance signal Σ side 2, 7 f. '1 is FM
As shown in FIG. 2, the demodulated signal generates a low hanging noise N that occurs during detracking.

"-Objective of the Invention" Therefore, the object of the present invention is that during playback across a plurality of tracks, noise similar to a synchronization signal is generated in the playback output during detracking, and this noise causes the spindle to move. An object of the present invention is to provide a video disk reproducing circuit which prevents malfunctions from occurring in the rotation servo of a motor.

"Summary of the Invention" The present invention provides a video disk playback circuit that plays back a video signal recorded on a disk-shaped recording medium by FM modulating the video signal. This is a video disk playback circuit that suppresses frequency components lower than the carrier frequency corresponding to the synchronization signal of the N-modulated high-frequency signal that is played back during detracking when the top is not scanned correctly.

"Embodiment" An embodiment of the present invention will be described below with reference to the drawings. In Fig. 7, 1, 2, 3, 4゜5 indicates the capacitor, 6, 7.8 indicates the coil, and the capacitor 1,
2, 3, 4.5 and the coil 6° 7.8 constitute a bandpass filter 38 shown surrounded by a broken line.

One end of the capacitor 1 is connected to an output terminal of an amplifier 10 via a resistor 9, and the other end of the capacitor 1 is connected to one end of a capacitor 2 and grounded via a coil 8.

The other end of the capacitor 2 is connected to one end of the coil 6 and grounded via the capacitor 3. The other end of the coil 6 is connected to one end of the coil 7 and grounded via the capacitor 4. The other end of the coil T is grounded via a capacitor 5 and connected to a connection point of a series connection of a resistor 11 and a resistor 12 inserted between a DC power supply terminal 14 and the ground. This bandpass filter 38 extracts the FM-modulated disc playback output.

An FET is connected to the connection point of this series connection of resistor 11 and resistor 12.
Thirteen gates are connected. The drain of FET'13 is connected to a DC power supply terminal 16 via a resistor 15, and also to one ends of a resistor 17 and a resistor 18. FET
130 source is connected to one end of resistor 19. resistance 19
A capacitor 21 and a coil 22 whose other ends are connected in parallel
connected to one connection point. The other connection point of the capacitor 21 and coil 22 connected in parallel is connected to one connection point of the capacitor 23 and coil 24 connected in parallel. The other of the capacitor 23 and coil 24 connected in parallel is grounded. These capacitors 21, 23 and coils 22, 24 constitute a tratsuno circuit for suppressing 2MI (z or less).

The other end of resistor 11 is connected to the base of transistor 25. A collector of transistor 25 is connected to DC power supply terminal 26 . The emitter of the transistor 25 is grounded via a resistor 2T and is also connected to the output terminal 28.

An FM demodulation circuit (not shown) is connected to this output terminal 28.

The other end of resistor 18 is connected to one end of coil 29. The other end of the coil 29 is connected to one end of the capacitor 30. The other end of capacitor 30 is connected to the emitter of transistor 31. This resistor 18, coil 29, capacitor 30
In this case, a 4.5 MHz to 5 MHz trap circuit is constructed. The collector of the transistor 31 is grounded,
The base of the transistor 31 is connected to the terminal 33 via the resistor 32.
connected to.

The base of a transistor 35 is connected to the terminal 33 via a resistor 34. The emitter of transistor 35 is amplifier 1
Connected to 0. The collector of transistor 35 is connected to amplifier 10 via capacitor 36. amplifier 10
An input terminal 37 is connected to the input terminal 37, and a reproduction signal read from the optical head and the disk is supplied to the input terminal 37. This amplifier 10 is composed of a resistor 18, a coil 29, and a capacitor 30.
When the MHz trap circuit is inserted into the circuit, that is, when the transistor 35 is turned on, the gain increases and it has high frequency compensation characteristics.

A low level control voltage is supplied to the terminal 33 during normal reproduction. When the control voltage supplied from the terminal 33 is low level, the transistor 31 and the transistor 3
5 is in the off state. Slave resistor 18 * Coil 29
．． The trap circuit composed of many capacitors 30 does not operate, and the gain of the amplifier 10 is reduced. Therefore, the reproduction signal of the optical head supplied from the input terminal 3T is transmitted to the 2M bandpass filter 38, which is shown surrounded by a broken line, and is composed of a capacitor 21.23 and a coil 22.24.
Bandwidth is limited via a trap circuit for suppressing frequencies below Hz. In FIG. 8, the frequency characteristic indicated by the solid line is the overall characteristic between the input terminal 37 and the output terminal 28 at this time.

Multiple optical heads are used to create search motions such as variable speed playback.

A high level control voltage is supplied to the terminal 33 when the operation across the track can be performed. When the control voltage supplied from the terminal 33 is at a high level, the transistor 31 and the transistor 35 are turned off. Therefore, the resistance 18,
A trap circuit composed of a coil 29 and a capacitor 30 is inserted into the circuit, and the amplifier 100 dyne increases.

For this reason, after the reproduced signal of the optical head supplied from the input terminal 37 is amplified by the amplifier 10, a signal of 2 MHz or less, which is composed of a band pass filter 38 shown surrounded by a broken line, a capacitor 21.23, and a coil 22.24, is transmitted. The band is limited through the suppression circuit, and furthermore, the resistor 18 and the coil 1
9. 4, 51viH composed of multiple capacitors 30
It is band limited via a trap circuit from z to 5 MHz. The overall frequency characteristic at this time is shown by the broken line in FIG.

Note that the trap circuit having a frequency of 4.5 MHz to 5 MHz may be inserted only when detracking the optical head.

``Effects of the Invention'' According to Jin's invention, when the optical head traverses the video disk and performs a playback operation, for example, when a search operation is performed, a frequency of 4.5
Since a trap circuit of MHz to 5 MHz is inserted,
When the optical head detracks, the lower sideband component of the color signal is suppressed. Therefore, the reproduced output signal during detracking is attenuated as shown in FIG. Therefore, no large-level signal components appear in the frequency components below the frequency fs corresponding to the sync output, and noise that hangs below the sync output level is prevented from occurring in the demodulated output. This prevents malfunctions in the rotation servo of the spindle motor when the optical head crosses multiple tracks to perform a reproducing operation, for example, during a search operation.
Alternatively, it is possible to prevent synchronization disturbances in the reproduced images from occurring at this time.

[Brief explanation of the drawing]

1, 2, 3, and 4 are waveform diagrams used to explain a conventional video disc playback circuit, and FIGS. 5 and 6 are spectral diagrams used to explain a conventional video disc playback circuit. FIG. 7 is a connection diagram of an embodiment of this invention, FIG. 8 is a frequency characteristic diagram used to explain an embodiment of this invention, and FIG.
The figure is a spectrum diagram used for detailed explanation of this invention. 10・・・・・・・・・Amplifier, 18・・・・・・・・・
...Resistor forming the trap circuit, 29...
・・・・・・Coil forming the trap circuit, 30...
......Capacitor forming the trap circuit, 28...Output terminal, 33...
......Control voltage input terminal, 37...-...
...Input terminal. Agent: Tomo Sugiura Figure 1 Figure 2 Figure 4

Claims (1)

Claims: A video disc reproducing circuit for reproducing a video signal recorded on a disc-shaped recording medium after the video signal is FM modulated. When reproducing across multiple tracks, at least the frequency component lower than the carrier frequency corresponding to the synchronization signal of the FM modulated high frequency signal reproduced during detracking when the tracks are not scanned correctly is suppressed. video disc playback circuit.