JPS6233374A - Tracking servo circuit - Google Patents

Abstract

PURPOSE:To improve a tracking performance by detecting a dropout from a reproducing signal of a pickup reproducing element and preventing a high frequency component from a filter circuit from being transmitted to a synthesizing means only during detecting the dropout. CONSTITUTION:A part of a reproducing signal taken out from a pickup circuit 3 is branched and supplied to a dropout detecting circuit 19. The reproducing signal is a multiple signal of a frequency modulated wave signal and a reference signal and during generating the dropout, its envelope is considerably deteriorated, so that the dropout detecting circuit 19 outputs a dropout detecting signal when the envelope of this reproducing signal is deteriorated below a prescribed level. This output signal is impressed to a switch circuit 18 as a switching signal. During an ordinary period on which the dropout is not generated, an input high frequency component of a terminal 18a is selected and outputted and during a detecting period of the generation of the dropout, the high frequency component is changed over and connected to a terminal 18b side and prevented from being transmitted to a phase compensating circuit 20. Thereby, the tracking performance can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Use The present invention relates to a tracking servo circuit, and in particular to a tracking servo circuit for accurately tracking and scanning a reproduction needle on a recording track of a disc-shaped rotating recording medium (disc). This invention relates to a dragging servo circuit that can reduce V.

Prior art The applicant of the present invention has previously disclosed in Japanese Patent Publication No. 59-21104 etc. that the main information signal and the first to third tracking control reference signals (hereinafter abbreviated as reference signals) can be obtained without forming a needle guide groove. The main information signal and the first to third reference signals are captured by electrostatic capacitance by a disk-shaped rotating recording medium having an electrode function recorded as a change in geometrical shape, and relative polishing scanning of the medium with a playback needle. We proposed a playback device that reads and plays as a variation of the above. In addition, the above-mentioned disc-shaped rotating recording medium (hereinafter referred to as a disk) proposed by the present applicant adds the same 14 signals to a digital modulated wave obtained by pulse code modulating a video signal or an audio signal, and converts it into a video signal. A compliant digital signal is recorded as the main information signal in four fields per rotation on a spiral main track, and the first and second signals are recorded at a lower frequency than the recording frequency band of the main information signal and have different frequencies. 2 reference signals rp+ and rp
2 are switched every rotation period of the recording medium, and are recorded with a sub-track formed in the middle between the adjacent main tracks in a burst pattern, and fP+, r
A third reference signal (index signal) fP3 for switching the tracking polarity of the tracking servo circuit is recorded at a switching connection portion of Pz at a level below a predetermined level so as not to affect the main information signal.

FIG. 2 is a diagram schematically showing the outline of the 1-rack pattern of this disc 1, where the spiral solid line indicates the center line of the spiral track (main track) on which the above information signal is recorded, and . The mark indicates the track (n1 track) where the first reference signal rp+ is recorded, and the X mark indicates the track (sub track) where the second reference signal fρ2 is recorded. As can be seen from FIG. 2, the reference signals rp+ and fl)2 are alternately switched every rotation period of the disk and one of the - reference signals is recorded, so that one piece of information addressed to the disk rotation is recorded. One of the reference signals rp+ and rPz is recorded on the outer circumferential side of the signal recording track, and the other reference signal is recorded on the inner circumferential side. For the information signal recording track,
Reference signal rPI.

The side on which rPz is recorded is switched for each track. For this reason, it is essential for normal tracking servo operation to distinguish which reference signal is recorded on the outer or inner side of the rack. The position indicated by diagonal lines in FIG. 2, that is, the reference signal fPI.

[The third track is located at the position corresponding to the recording switching position of ρ2.
The reference signal fP3 is recorded as an index signal.

The above reference signals rp+ to fP3 are selected to have a single frequency within an empty frequency band below the recording frequency band of the information signal, and are different from each other, and the reference signals rp+ and rpz are Each of the signals is recorded intermittently at a fixed period (for example, one horizontal scanning period), and the reference signal rP3 is continuously recorded over a fixed period. The disc 1 with the overlapping track pattern is, for example, 90
The recorded information signal is rotated at 0rpH1.
It is read and reproduced as a change in capacitance.

The tracking servo circuit in the playback device for the disc 1 discriminates and separates the reference signals fP and rPz from the playback signal, performs envelope detection on them, and further converts the envelope detection signals into differential signals using a differential amplifier. Amplify the tracking error signal and supply it to the tracking coil through the phase compensation circuit, drive circuit, etc.
It has a closed-loop configuration that minimizes track deviation in the track width direction of the playback button, called a playback button. As a result, the regeneration needle is caused to scan on the main track shown by the solid line in Figure M2.

Here, the above-mentioned tracking error signal has a waveform as shown in FIG. High frequency components due to distortion and dropouts are superimposed. In particular, dropout causes the tracking servo circuit to become an oven loop, and the loop gain increases, so that even if the high frequency component changes sharply, it disturbs the tracking of the reproduction needle even if the dropout is small. Therefore, in order to prevent this, it is possible to increase the loop gain of the tracking servo circuit, but if the loop gain is decreased, a tracking control operation that sufficiently follows track deviation due to disk eccentricity or distortion cannot be performed.

Therefore, in the conventional tracking servo circuit, the loop gain must be set relatively high.

Problems to be Solved by the Invention However, in the conventional tracking servo circuit described above, the peak value of the tracking error signal is large for a disk with a large eccentricity, and the value during the muting period ( This has a large difference from the center level (zero level) of the tracking error signal after a certain time constant, and when muting is released, a large drive signal is supplied to the tracking coil, which may conversely cause a tracking error. There was a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a tracking servo circuit that solves the above problems by muting only the high frequency components of the dragging error signal when dropout occurs.

Means for Solving the Problems The tracking servo circuit according to the present invention includes a filter circuit that divides the band of a tracking error signal into two and outputs a low frequency component and a high frequency component, respectively, and a filter circuit that divides the band of a tracking error signal into two and outputs a low frequency component and a high frequency component, and A synthesizing means that performs additive zero synthesis after extensively phase-compensating the component and the high frequency component separately, and the output signal of this synthesizing means is used as a tracking error signal to displace the pick-up reproducing element in the track width direction and send it to a racking coil. a detection circuit for detecting a dropout from the reproduction signal of the pickup reproduction tree; and an output detection signal of the detection circuit to block transmission of the aha frequency component from the filter circuit to the synthesis means only during the dropout detection period. This is a muting means.

Operation The low frequency components extracted from the above filter circuit are low frequency components that include at least 6 frequencies (for example, 15 Hz) that are the reciprocal of one rotation period of the disc-shaped rotating recording medium (disk), and this is mainly a low frequency component that is It changes depending on the eccentricity of. Signals with large amplitudes and large displacements in the tracking error signal are mainly composed of this low frequency component.
Changes are gradual. On the other hand, the high frequency components extracted from the filter circuit described above are due to dropouts and disk distortion, and although the amplitude is small, the changes are rapid and are likely to cause tracking errors. Also, this 7X
The low frequency components are used to correct slight track deviations that cannot be corrected with the low frequency components.

Therefore, by detecting a dropout that tends to cause a sharp change in high frequency components by the detection circuit, and using the detection signal to mute only the high frequency components by the muting means, the filter is filtered during the dropout detection period. Since the tracking servo operation is performed based only on the low frequency components from the circuit, tracking performance is improved.

Embodiment An embodiment of the present invention will be described below with reference to the block system diagram shown in FIG. In the figure, a disk having a track pattern as shown in FIG. 2, placed on a turntable (not shown), is rotated at, for example, 900 rpm.
The regenerating needle 2, called a sensor, slides on its surface. As a result, the capacitance formed between the disk 1 and an electrode (not shown) fixed by vapor deposition on the rear end surface of the regenerator 2 changes in accordance with the recorded information signal. The pickup circuit 3 consists of a resonant circuit whose resonant frequency changes according to changes in this capacitance, a circuit which applies a constant frequency to this resonant circuit, and an amplitude which changes according to changes in the above-mentioned capacitance from the resonant circuit. It consists of a circuit that amplitude-detects a high-frequency signal, and a circuit that pre-amplifies this amplitude-detected high-frequency signal (reproduction signal). The information signals (for example, video signals and audio signals) of the information signal recording track are demodulated respectively, while a part is branched and sent to bandpass filters 5 and 6 and f
The signals are supplied to the P3 detector 7, respectively.

The fp3 detector 7 selects the frequency of the third reference signal fP from the reproduced signal, generates an fP3 detection signal phase-synchronized therewith, and applies it to the switching pulse generator 8. Furthermore, the bandpass filter 5 selects the frequency of the first reference signal [ρ1] from the reproduced signal to
On the other hand, the bandpass filter 6 selects the frequency of the second reference signal fP2 from the reproduced signal and applies it to the second input terminal of the switching circuit 9.

The switching circuit 9 is switched by a switching pulse from the switching pulse generator 8,
For example, during the period when the switching pulse is at a high level, each output terminal of the bandpass filter 5.6 is connected to each input terminal of the detection circuit io, 1i, and on the other hand, during the period when the switching pulse is at a low level, each output terminal of the bandpass filter 5.6 is connected to each input terminal of the detection circuit io, 1i. are separately connected to each input terminal of the detection circuit 11.10.

The switching pulse from the switching pulse generator 8 has its polarity and period changed in response to the reproduction mode signal inputted from the control panel via the input terminal 12, and the switching pulse is changed in polarity and period from the detection signal from fρ3 detection': S7 or The polarity is reversed when a kick pulse to the drive circuit 21 (excluding kick pulses input during the fP3 reproduction 11), which will be described later, is generated. In this way, the envelope detection output of the reference signal reproduced from the outer track of the main rack to be reproduced is extracted from the detection circuit 10, and the envelope detection output of the reference signal is extracted from the inner track of the main track to be reproduced. The envelope detection output of the reference signal reproduced from the track is extracted,
It is applied to the next stage differential amplifier 13. A tracking error signal is extracted from the differential amplifier 13, which has a polarity corresponding to the track deviation direction with respect to the main track of the regenerator 2 and a level corresponding to the track deviation length.

Both of these tracking error signals are processed by a low-pass filter 1 whose cutoff frequency is selected to be, for example, about 60 to 100 Hz.
4 and a high-pass filter 15, and the band is divided into two. The low frequency component extracted from the low pass filter 14 is supplied to an adder circuit 17 after receiving a predetermined phase compensation by a phase compensation circuit 16 . The high frequency component extracted from the high pass filter 15 is supplied to the terminal 18a of the switch circuit 18.

On the other hand, a part of the reproduced signal taken out from the pickup circuit 3 is branched and supplied to the dropout detection circuit 19. Here, the above-mentioned reproduced signal is a multiplexed signal of the frequency-modulated wave signal and the reference signals "ρl, rP2," and when a dropout occurs, its envelope drops significantly, so the dropout detection circuit 19 detects this reproduced signal. When the envelope of the dropout falls below a predetermined level, it is detected as a dropout and a dropout detection signal is output.The output signal of the dropout detection circuit 19 is applied as a switching signal to the switch circuit 18, and the dropout is detected. During a normal period in which the dropout is not detected, the high frequency component input to the terminal 18a is selectively output, and during a dropout detection period, the terminal 18b is switched and connected to prevent transmission of the high frequency component to the phase compensation circuit 20. During a normal period when dropout does not occur, the high frequency component extracted from the switch circuit 18 is supplied to the phase compensation circuit 20,
After receiving a predetermined phase compensation here, the signal is supplied to the adder circuit 17.

The phase by the adder circuit 17? After the low frequency components and high frequency components from the 111 compensation circuit 16.
is supplied, and the reproducing meter 2 is displaced in the radial direction of the disk 1, that is, in the track width direction, in a direction that corrects the track deviation, at a displacement end that minimizes the track deviation.

On the other hand, when dropout occurs, as described above (the switch circuit 18 blocks the transmission of high frequency components to the phase compensation circuit 20. As a result, only the low frequency components are taken out from the adder circuit 17 and sent to the drive circuit). 21 to the tracking coil 22, and the regenerator 2 is roughly tracked by only the low frequency components.

Therefore, if the dropout disappears after a relatively short IJ and the normal playback state is restored, and the above-mentioned muting is canceled, tracking errors are less likely to occur. Note that the playback signal becomes 1 due to the
However, if the dropout continues, the low frequency components of the dropout will gradually become unobtainable with a human time constant. Does not disappear completely.

Note that the present invention is not limited to the above-described embodiments, and for example, a disc to be reproduced may not have a tracking control reference signal fp+-fp3 recorded thereon, and a reproduction apparatus that reproduces the reference signal fp+-fp3 using a light beam. Of course, the present invention can be applied to a tracking water circuit.

Effects of the Invention As described above, according to the present invention, the tracking error can be reduced during the muting period of the tracking error signal or immediately after muting is released, and the tracking performance can be improved. It is.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the circuit of the present invention;
FIG. 2 is a diagram showing an example of a track pattern of a disk-shaped rotating recording medium, and FIG. 3 is a diagram showing an example of a tracking error signal waveform. DESCRIPTION OF SYMBOLS 1... Disc-shaped rotating recording medium (disc), 2... Playback needle (1 sensor), 5.6... Bandpass filter, 7...
・fP3 detector, 9... switching circuit, 10°1
1... Detection circuit, 13... Differential amplifier, 17'I.
...Low pass filter, 15...High pass filter, 17...
・Additional circuit, 18... Switch circuit, 19... Dropout detection circuit, 22... 1 ~ Rucking coil.

Claims (1)

[Claims] Tracking in which the pickup/reproduction element is displaced in the track width direction so that the track deviation is minimized by a tracking error signal generated based on a signal indicating the track deviation of the pickup/reproduction element with respect to the information signal recording track on the disc-shaped rotating recording medium. In the servo circuit, a filter circuit divides the band of the tracking error signal into two and outputs a low frequency component including at least one rotation period of the disc-shaped rotating recording medium and a high frequency component having a higher frequency. , a synthesizing means for adding and synthesizing the low frequency component and the high frequency component from the filter circuit after separately phase compensating them, and using the signal extracted from the synthesizing means as a tracking error signal to drive the pickup reproducing element. means for supplying a signal to a tracking coil that is displaced in the track width direction; a detection circuit that detects a dropout from the reproduction signal of the pickup reproduction element; muting means for blocking transmission of the high frequency component to the synthesizing means, and performing tracking servo operation based only on the low frequency component from the filter circuit during the dropout detection period. Features a tracking servo circuit.