JPS62162286A - Tracking servo circuit - Google Patents

Abstract

PURPOSE:To hold tracking following capacity even when foreign matters are stuck to a disk or a sensor by generating the 2nd pulse only in a pulse period indicating pulse width more than a prescribed value in a pulse corresponding to a drop-out generating period and controlling gain so that the loop gain of a tracking servo circuit is increased. CONSTITUTION:A detecting circuit 34 detects an FM signal (a) outputted from a buffer amplifier 32 as a signal (b) and a comparator 35 generates a signal (c) to be turned to the high level in a drop-out generating period. An integrating circuit 37 integrates the input signal (c) and a comparator 42 generates a signal (h). A monostable multivibrator 44 generates a signal having several hundred ms pulse width time and an OR circuit 45 generates a signal (i). An integrating circuit 46 generates a signal (j) and a voltage control amplifier 33 amplifies a tracking error signal outputted from a phase compensating circuit 27 in accordance with the pulse period of the input signal (j) and supplied the amplified signal to a tracking coil 24 through a driving circuit 22.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a tracking servo circuit, and more particularly to a tracking servo circuit that allows a sensor to accurately follow and scan a recording track of a rotating recording disk.

Conventional technology Conventionally, disks on which information signals are recorded in a spiral manner by countless intermittent pits have been recorded using a sensor with electrodes.
There is a playback 1ffi that reads and plays according to changes in the capacitance a1 formed between the playback needle and the disk. A frequency spectrum signal not shown in FIG. 4 is recorded on a disc read and reproduced by such a reproduction apparatus. In the figure, ■ is the FM luminance signal band, and ■ is the FMIIa color signal side band.

■ is the audio signal sideband, IV is the reference signal fPl~
Bands of fP3 are not shown.

Here, a video signal and an audio signal are recorded as main information signals in four fields per revolution on a spiral main track of the disk. Further, the reference signals (tracking signals) fPI and fP2, each having a single frequency different from each other at a frequency lower than the recording frequency band of the main information signal, are switched each time the disk rotates, and are adjacent to each other in a burst pattern. A sub-track is recorded adjacent to the above-mentioned main track, and furthermore, a reference signal (index signal) for switching the tracking polarity of the tracking servo circuit is provided at the switching connection portion of the reference signals fPI and fP2.
fP3 is recorded.

FIG. 5 shows a block diagram of an example of a conventional tracking servo circuit. In the figure, a high-frequency frequency modulated reproduction signal (FM signal) reproduced by a sensor (not shown) is filtered through a low-pass filter 1 (for example, a cutoff frequency of 1M
Hz), the main information signal is removed, and the reference signals fPI to fP3 are converted into P waves and output as the tracking control signal 2. The tracking control circuit 2 includes an automatic gain control amplifier (AGC amplifier)3. Amplifier 4. Tank circuit and amplifier5. Limiter 6, tank circuit 7° high frequency amplifier (RF amplifier) 8. AGC detection circuit 9, switch circuit 10. Amplifier 11. The reference signal fp+-fp3 from the low-pass filter 1 is supplied to the AGC amplifier 3.

Here, the reference signal fP3 is the AGC amplifier 3° amplifier 4
．． Bandpass filter 14. The signal is supplied to a mechanical controller (not shown) that controls the mechanism of the disc playback device through a parallel circuit consisting of a tank circuit, an amplifier 5', a noise filter 15, and a regenerator 16.

On the other hand, the reference signals f' p + and U f P 2 Ge
t, after the abnormal level is removed from the AGC unit 3 via the limiter 6, it is extracted by the tank circuit 7 having the synchronized circuits 7a and 7b, respectively. The reference signals fPI and fP2 outputted from the tank circuit 7J are supplied to the 〇〇 amplifier 3 via the RF amplifier 8 and the AGC detection circuit 9, thereby increasing the average level of the reference signals fPl and fρ2. Used as an AGC control signal.

Furthermore, the output reference signals fPI and fP of the tank circuit 7 are
2 are supplied to detection circuits 17 and 18, respectively, via a switch circuit 10 and an amplifier 11 which are switched in response to a switching signal from the mechanical controller, and are detected here and then output to an error amplifier 19. The error amplifier 19 generates a tracking error signal according to the level difference between the incoming output signals of the detection circuits 17 and 18, that is, the level difference between the reference signals fPI and fP2, and outputs the tracking error signal via the phase compensation circuits 20 and 21. It is output to the drive circuit 22 and a feed motor (not shown).

On the other hand, the kick pulse from the mechanical controller is sent to the mixing circuit 23.
The drive circuit 22 converts the incoming tracking error signal into the required power and applies it to the tracking coil 24.

In this way, the playback needle is placed in the radial direction of the disk.
It is displaced in the direction and displacement h1 for correcting the track deviation, and the reproduction is controlled so that it is always on-track.

Problems to be Solved by the Invention Incidentally, in a tracking servo system in a disk playback device, a closed loop consisting of a disk, a sensor (playback needle), and an electric circuit (tracking servo circuit) is generally established. The closed loop gain may change due to factors such as the matching state between the sensor and the disk and variations in the electric circuit. In this case, it is known that the amount of change in loop gain is as much as ±5 to ±6 in total.

In order to solve this problem, the applicant first proposed the
In Japanese Patent No. 61555, a tracking servo circuit was proposed in which the loop gain was corrected according to fJ+ so that it always remained substantially constant.

This tracking servo circuit includes a signal m superimposition circuit that superimposes a signal with a constant amplitude and a constant frequency in a frequency band lower than the information signal recording band of the information signal recording track on the 1-racking error signal, and A filter circuit that separates the signal of the constant frequency from the input tracking error signal of the circuit as a P wave, and a signal of the constant frequency among the input tracking error signal of this filter circuit based on the envelope detection level of the output signal of this filter circuit. and automatic gain control means for controlling the level of the reproduction signal of the pickup reproduction element so that the level of the reproduction signal is maintained at a substantially constant level.

However, even in the above-mentioned conventional tracking servo circuit, there is a problem in that if foreign matter such as dust or water droplets adheres to the surface of the disk or the sensor, the closed loop is likely to be broken, and the loop gain will drop sharply. Ta.

In this case, foreign matter adheres to the disk or sensor, causing the sensor to rise above the surface of the disk.
The output FM signal level of the sensor decreases. Among these FM signals, the video signal recorded by frequency modulation (FM) is
Even if the output of the sensor decreases to some extent, processing such as amplification and limit width is performed in the subsequent circuit, so that the decrease in the sensor output (121) is unlikely to appear on the screen. However, since the tracking signals fPI and fP2 are amplitude information, the influence of a decrease in sensor output is too large to be ignored. Therefore, if foreign matter adheres to the disk or the sensor, there is a problem in that the loop gain decreases and the tracking ability decreases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a tracking servo circuit that solves the above problems by detecting the presence of foreign matter on the disk surface or sensor and increasing the loop gain.

Means for Solving the Problems A tracking servo circuit according to the present invention detects a dropout in a reproduction signal reproduced by a sensor, and generates and outputs a first pulse having a pulse width corresponding to the period during which the dropout occurs. a first pulse generating means; a second pulse generating means for generating and outputting a second pulse only in response to a pulse period in which the pulse width is equal to or greater than a predetermined value during the first pulse; It is equipped with a voltage control amplifier whose gain is controlled to increase the loop gain of the tracking servo circuit only for the next period, and supplies the output tracking error signal of the voltage control amplifier to the tracking coil to control the sensor so that the tracking deviation is minimized. It is configured to be displaced in the track width direction so that

If foreign matter adheres to the working disk or the sensor, the output playback signal of the sensor will be reduced and dropout will occur.

Here, the first pulse generating means detects this dropout, generates a first pulse having a pulse width corresponding to the dropout occurrence period, and outputs it to the second pulse generating means by 1°.

The second pulse generating means generates a second pulse corresponding to a pulse period whose pulse width is equal to or greater than a predetermined value among the pulses included in the first pulse. In other words, the output FM signal of the sensor has a large duration depending on the alignment between the sensor and the disk.

Although a small dropout occurs, the occurrence of this large dropout is detected by the second pulse generating means, and a second pulse corresponding to this large dropout is generated. . The second pulse is fed to a voltage controlled amplifier where it controls the gain. The output tracking error signal of this voltage control amplifier is supplied to a tracking coil, thereby performing tracking control of the sensor.

In this way, the reduction in the loop gain due to foreign matter adhering to the disk or sensor is compensated for, thus 1-
Rucking tracking ability is maintained.

Embodiment FIG. 1 shows a block system diagram of an embodiment of a tracking servo circuit according to the present invention. In the figure, the same components as in FIG. 5 are given the same reference numerals.

Here, as described later, the detection circuit 34. Comparator 35
and the reference voltage source 36 correspond to the first pulse generating means, and the integrating circuit 37 . Comparator 42, reference voltage source 43
．． The monostable multivibrator 44 and the OR circuit 45 correspond to the second pulse generating means, respectively.

Further, the GC circuit 25 corresponds to the AGC amplifier 3° AGC detection circuit 9, etc., and the subtracter 26 corresponds to the error amplifier 1.
9, and the phase compensation circuit 27 corresponds to the phase compensation circuit 20.
and 21, respectively, so the description of these will be omitted as appropriate below.

Before explaining the circuit of the present invention, the structure of the cartridge controlled by the circuit of the present invention will be briefly explained in the third drawing. In FIG. 3, the sensor (regeneration needle) 29 is fixed to one end of the cantilever 28, and this sensor 29 is connected to an electrode (not shown) via a lead wire.

Further, four sets of the tracking coils 24 are provided on both sides of the other end of the cantilever 28, and a stretcher coil 30 is provided in the axial direction of the other end of the cantilever 28. Furthermore, a needle pressure coil 31 is provided above the other end of the cantilever 28 . Therefore, the tracking coil 24 displaces the sensor 29 in the direction of arrow A or B (i.e., the track width direction) so that the track deviation is minimized, and the sensor 29 is moved by the tracking coil 24 in the direction of arrow A or B (i.e., in the track width direction). letcher coil 30
As a result, the sensor 29 is displaced in the direction of arrow C or D (i.e., in the track direction) so that jitter is minimized, and further, the stylus pressure coil 31 moves the sensor 29
is displaced in the direction of arrow E or F, and the sensor 29
The stylus pressure against the disc is controlled.

In this embodiment, as will be described later, only the tracking coil 24 and the g1 pressure coil 31 are used to connect the sensor 2.
9 in the directions of arrows A or B and E or F, and the jitter correction by the stretcher coil 30 is not performed.

Returning to FIG. 1 again, the FM signal a as shown in FIG. . The reference signal fP3 is made into a P wave by the bandpass filter 14 and output to the mechanical controller, while the reference signal fP
I and fP2 are AGC circuit 25. It is supplied to the subtracter 26 via the tank circuit 7 and the detection circuits 17 and 18.

The reducer 26 generates the tracking error signal according to the level difference between the incoming reference signals fPl and fpz, and supplies it to the voltage control amplifier 33 via the phase compensation circuit 27.

On the other hand, the detection circuit 34 receives the FM signal from the buffer amplifier 32.
The signal a is detected and outputted to one input terminal of the comparator 35 as a signal shown in FIG. 2(B). The comparator 35 compares the reference voltage from the reference voltage source 36 supplied to the other input terminal with the level of the output signal of the detection circuit 34, and calculates the FM signal as shown in FIG. 2(C).
Dropout occurrence period of signal a (i.e., time t1
~ j2. t, + to t6 and t9 to i+o) is generated and outputted to one input terminal of the integrating circuit 37° monostable multivibrator 38 and OR circuit 39, respectively.

The monostable multivibrator 38, as shown in FIG.
A signal d that is triggered by IO, etc. and becomes high level at times t2 to t3, t6 to t8, and t to "t12, etc., is generated and output to the other input terminal of the OR circuit 39. Thereby, the OR The circuit 39 operates at times t+-t3.'j4 to t8 and t9 to t1, as shown in FIG.
Generates a signal e that becomes high level at the second etc. and integrates the circuit 4.
Output to 0. The integrating circuit 40 integrates the incoming signal e to generate a signal f as shown in FIG.

In this way, the sensor 29 is displaced in the direction of the arrow F in accordance with the level of the signal f during the high level period of the signal f (that is, during the dropout period of the FM signal a). The stylus pressure between 29 and the disk is increased. This improves the above-mentioned condition in which the sensor 29 is raised above the surface of the disk due to foreign matter adhering to the disk or the sensor, thereby compensating for the drop-out of the FM signal a.

The integration circuit 40 is provided to prevent the stylus pressure of the sensor 29 from suddenly increasing due to dropout of the FM signal a, and to increase the stylus pressure gradually.

On the other hand, the integrating circuit 37 has a time constant of several ms, for example, and integrates the incoming signal C to generate a signal q as shown in FIG. Output to the terminal. The comparator 42 compares the reference voltage from the reference voltage source 43 supplied to the other input terminal with the level of the output signal q of the integrating circuit 37, and compares it with the level of the output signal q of the integrating circuit 37.
''), a signal that becomes high level is generated at times t5 to t7, etc., and is applied to one input terminal of the monostable multivibrator 44 and the OR circuit 45, respectively.

The signal 1 changes its level during each dropout period of the FM signal a, depending only on the major dropout period. In other words, the integration circuit 37. The comparator 42 and the reference voltage source 43 will detect a large dropout event (or large defect) during each dropout of the FM signal a. This allows FM
Due to a small dropout (or short defect) of the signal a, the loop gain is prevented from being changed frequently, as will be described later.

The monostable multivibrator 44 is triggered at the falling edge time t7 of the incoming signal, and generates a signal having a pulse width time of, for example, several hundred ms, and outputs it to the other input terminal of the OR circuit 45. As a result, the OR circuit 45
As shown in FIG. 2(I), a signal i that becomes high level at times t5 to tI+ is generated and output to the integrating circuit 46. Integrating circuit 46 integrates the incoming signal i to obtain a second signal i.
A signal j as shown in FIG. LJ) is generated and output to the voltage control amplifier 33. The voltage control amplifier 33 amplifies the tracking error signal from the phase compensation circuit 27 according to the pulse period of the incoming signal j, and amplifies the tracking error signal from the drive circuit 22.
The signal is supplied to the tracking coil 24 via. In this way, the loop gain is controlled.

The integrating circuit 46 is provided to prevent the closed loop gain from increasing rapidly due to a large dropout of the FM signal a, and to change the gain gradually.

In this way, if a dropout occurs in the FM signal a due to foreign matter adhering to the surface of the disk or the sensor 29, this will be detected, and if there is a short defect, only the stylus pressure servo will be applied and the disk and sensor 29 will be detected. When a large defect occurs, the tracking ability of the sensor 29 is restored by changing the stylus pressure and loop gain.

Note that the monostable multivibrators 38 and 44 are
Of course, other pulse generating means may also be used.

Effects of the Invention As described above, according to the present invention, the loop gain is increased by detecting the presence of foreign matter on the surface of the disk or the sensor. When the output level of the sensor decreases, the adhesion between the disc and the sensor can be restored, and the tracking ability of the sensor can be maintained, so tracking errors can be prevented. has.

[Brief explanation of drawings]

FIG. 1 is a block system diagram showing one embodiment of the tracking servo circuit according to the present invention, FIG. 2 is a signal waveform diagram for explaining the operation of the block system shown in FIG. 1, and FIG. 3 is a perspective view showing the configuration of a cartridge. , FIG. 4 is a frequency spectrum diagram of a signal recorded on a disk, and FIG. 5 is a block system diagram showing an example of a conventional tracking servo circuit. 1...Low pass filter, 7...Tank circuit, 17°1
8.34...Detection circuit, 22...Drive circuit, 2
4...Tracking coil, 25...AGC circuit,
26... Subtractor, 27... Phase compensation circuit, 28...
・Cantilever, 29...Sensor (regenerated needle), 30
...stretcher coil, 31...needle pressure coil,
32... Buffer amplifier, 33... Voltage control amplifier, 35°42... Comparator, 36.43... Reference voltage source, 37.40.46... Integrating circuit, 38.4
4... Monostable multivibrator, 39.4.5...
・OR circuit, 41...output terminal. Patent Office Commissioner Michibe Uga for each procedural amendment 1, Indication of the case 1986 Patent Application No. 3299 2, Name of the invention Tracking Nervo Circuit 3, Person making the amendment Relationship with the case Patent applicant address 221 Kanagawa 3-12 Moriyamachi, Kanayō-ku, Yokohama City, Prefecture Name (432) Japan Victor Co., Ltd. Representative Director and President Michi Shishi - Department 4, Agent Address 5-7 Kojimachi, Chiyoda-ku, Tokyo 102 Telephone 03 (263> 3271) Number (representative) spontaneous correction
1+, , 67.2, 206, column for detailed description of the invention in the specification subject to amendment. 7. Contents of correction In the specification, "jitter correction" written on page 12, line 11 is corrected to "correction to jitter correction."

Claims (1)

[Claims] A tracking error signal generated based on a signal indicating the track deviation of the sensor with respect to the information signal recording track on the rotating recording disk causes a dropout of the reproduced signal reproduced by the sensor in a closed-loop tracking servo circuit that controls the sensor. a first pulse generating means that detects and generates and outputs a first pulse with a pulse width corresponding to a dropout occurrence period; a second pulse generating means for generating and outputting a second pulse;
and a voltage control amplifier whose gain is controlled to increase the loop gain of the tracking servo circuit only during the input period of the second pulse, and supplies an output tracking error signal of the voltage control amplifier to the tracking coil. A tracking servo circuit characterized in that the sensor is configured to be displaced in the track width direction so that the track deviation is minimized.