JPS60117462A - Information reproducing device - Google Patents

Abstract

PURPOSE:To make it difficult that tracking control is disturbed by a defect of an information recording carrier, by switching the time constant of a high-pass filter to a small value when a defect is detected in a reproduced part of the information recording carrier and cancelling quickly a speed error just after detection when noise is mixed into a control signal just before detection because of delay of defect detection to generate the speed error in an actuator. CONSTITUTION:If a defect detection signal is outputted when a defective part of an information recording carrier 1 is tracked, a changeover switch 8 switches the signal to be inputted to a high-pass filter 12 from the error signal outputted from an error detecting circuit 5 to the output signal from a low-pass filter 11 and switches the time constant of the high-pass filter 12 to a small value. Thus, even if an impulsive noise remains because of delay of defect detection, the speed error due to this noise is canceled just after detection to stabilize tracking.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an information reproducing apparatus that reads information from an information recording carrier on which information is recorded on concentric or spiral information tracks.

Conventional Structure and Problems As the recording density of an information recording carrier on which information is recorded on concentric or spiral information tracks increases, tracking control is generally required for an information reproducing apparatus. Such information recording carriers are already known, such as optical video disks, digital audio disks, other data files, capacitive video disks without grooves, and high-density magnetic disks with data surface servo. With such an information recording carrier, high-density recording and reproduction is possible by performing tracking control during reproduction. However, if there is a defect in the information recording carrier, and this defect causes the information track to disappear or a large amount of noise is mixed into the tracking control signal, there is a drawback that the tracking control is easily lost and jumps to a nearby information track. . This tendency is particularly noticeable in optical digital audio discs where the linear velocity of the information track is slow because the transit time for the defective portion is long. In order to improve these drawbacks, a method has already been proposed in which a defect in an information record carrier is detected and the immediately preceding low frequency component value is held while the defective portion is being tracked.

FIG. 1 is a block diagram showing an example of tracking control means in a conventional information reproducing apparatus using the above method.
is an information recording carrier, 2 is a playback head, 3 is a preamplifier, 4
5 is a defect detection means, 5 is an error detection circuit, 6 is a low-pass filter, 7 is a hold circuit 8 is a changeover switch, 9 is a drive circuit, and 10 is an actuator.

The operation of the tracking control means of the information reproducing apparatus configured as described above will be explained below. FIG. 2 is a signal waveform diagram for explaining the operation of the tracking control means, which shows (a), (b), (c), (d),
and (e) are A and B in FIG. 1, respectively.

This corresponds to points C, D, and E. First, a case will be described in which a normal portion of the information recording carrier with no defects is tracked. The reproducing head 2 reads the information signal from the information recording carrier 1 and detects a relative positional error, that is, a tracking error, between the information track and the reproducing head 2, which occur due to the rotation of the information recording carrier 1 or disturbance vibration. outputs a tracking error detection signal. The error detection circuit 5 receives the above racking error detection signal, extracts a tracking error component, performs processing such as differential compensation as necessary, and outputs a tracking error signal. This tracking error signal is transmitted to the changeover switch 8.
The signal is input to the drive circuit 9 through. The actuator 10 moves part or all of the reproducing head 2 based on the output signal of the drive circuit 9, thereby performing tracking.

On the other hand, when there is a defect in the information recording carrier 1 and the defective portion is to be tracked, the process is as follows. Figure 2 (a
) is the reproduced signal at this time, and as shown in the figure, abnormalities such as a drop in amplitude occur. Δt shown in the figure indicates the time during which the defective portion of the information recording carrier 1 is being reproduced. The defect detection means 4 detects such an abnormality in the reproduced signal and outputs a defect detection signal.

When tracking this defective portion, generally no error signal is obtained, and pulse-like noise may be generated when entering and exiting the defective portion. FIG. 2(c) shows an example of such an error signal. When tracking such a defective part, a defect detection signal is output, and in response to this, the hold circuit 7 holds the low-frequency component of the error signal extracted by the low-pass filter 6, and the changeover switch 8 is activated. The input signal to the circuit 9 is switched from the error signal to the hold signal held by the hold circuit 7. The low-frequency component of the error signal extracted by the low-pass filter 6 is a signal as shown in FIG. 2(d),
Therefore, the input signal to the drive circuit 9 is as shown in FIG. 2(e). By holding in this way, the effect of the error signal disappearing during the defective portion transit time can be prevented.

However, in such a conventional configuration, since there is a time delay Td in the detection of a defect by the defect detection means 4, the second
As shown in Figure (e), pulse noise that occurs when entering a defective portion often remains without being removed. In such a case, the actuator IO is accelerated by this pulsed noise and causes a speed error, so the tracking error increases while the actuator IO passes through the subsequent defective part, and there is a drawback that track jumps are likely to occur. Ta.

OBJECTS OF THE INVENTION An object of the present invention is to eliminate the above-mentioned conventional drawbacks and to provide an information reproducing apparatus capable of stable tracking control against defects in an information recording carrier.

Structure of the Invention The information reproducing apparatus of the present invention includes an information reading means for reading information from an information recording carrier in which information is recorded on concentric or spiral information tracks, and an information reading position of the information reading means relative to the information track. an error detection means for detecting a positional error; a tracking control means comprising a closed loop for correcting the information reading position according to an error signal outputted from the error detection means; and a tracking control means for detecting a defect in the information recording carrier. and a defect detection means for outputting a defect detection signal when the information reading position substantially passes through the defect, and the tracking control means passes through a high frequency component of the error signal to obtain a high frequency error signal. a high-pass filter; a low-pass filter having a passband gain of 1 and connected substantially in parallel with the high-pass filter, passing a low-frequency component of the error signal to obtain a low-pass error signal; an addition means for adding the low-pass error signal and the wide-pass error signal again; and a changeover switch for switching the high-pass filter so that the output signal of the low-pass filter is input to the high-pass filter according to the defect detection signal. The high-pass filter is configured such that its time constant is switched to a small value in response to the defect detection signal, so that tracking control is unlikely to be disturbed even if there is a large defect in the information recording carrier. This enables stable tracking.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 shows a block diagram of a tracking control device in an embodiment of the present invention. In Figure 3, 1
1 is a low-pass filter whose pass band has a gain of 1, and 12 is a high-pass filter 13 is an adder.

The operation of the tracking control device of this embodiment configured as described above will be described below.

FIG. 4 is a signal waveform diagram for explaining the operation of this tracking control device. (a), (b), (C) in the same figure
, (d), and (e) are A, B, and C in Figure 3, respectively.
, D and E points. In a normal part of the information recording carrier 1 without defects, the error signal is divided into a low-pass error signal and a high-pass error signal by a low-pass filter 11 and a high-pass filter 12. 13 and then supplied to the drive circuit 9, it is essentially the same as if the error signal is directly supplied to the drive circuit 9, and its operation is almost the same as in the conventional example.

On the other hand, when there is a defect in the information recording carrier 1 and the defective portion is tracked, an abnormality such as a drop in amplitude appears in the reproduced signal as shown in FIG. 4(a). As in the case of FIG. 3, Δt shown in the figure indicates the time taken to pass through a defective portion of the information recording carrier. The defect detection means 4 detects such an abnormality in the reproduced signal and outputs a defect detection signal. When tracking such a defective part, a defect detection signal is output, and in response to this, the changeover switch 8 changes the signal input to the high-pass filter 12 from the error signal output from the error detection circuit 5. The time constant of the high-pass filter 12 is also switched to a small value while switching to the output signal from the low-pass filter 11. In this way, even if pulse noise remains due to a delay in defect detection, the speed error caused by this noise can be immediately canceled out, and tracking can be stabilized. The reason for this will be explained in detail below.

In general, the displacement of the information track is gradual, and it can be considered that there will be no sudden displacement unless abnormal vibrations are applied, and in that case, accurate tracking will be performed if the actuator IO moves faithfully in accordance with the low-frequency error signal. However, if pulse noise is added when entering the defective part, extra energy is generated by the actuator 10 due to this noise.
will be added to.

If the order and constant are set so that the output of the low-pass filter 11 hardly responds to the above-mentioned pulse noise, and the gain of the passband is set to 1, the magnitude of this extra energy can be reduced by using the low-pass error signal as a reference. It is proportional to the time-integrated value of the amplitude of the error signal for this. At this time, since most of the above-mentioned pulse noise is included in the high-pass error signal, if the input signal to the high-pass filter 12 is switched to the low-pass error signal, the error with respect to this low-pass error signal is The high-frequency error signal is swung in the opposite direction to the above-mentioned pulse noise so as to cancel out the integral value of .

However, since the low-pass filter 11 needs to have a sufficiently low cutoff frequency to be able to sufficiently remove the noise components of the tracking error signal, including the above-mentioned pulse noise,
Correspondingly, the time constant of the high-pass filter 12 is also normally set to a large value. Therefore, the extra energy caused by the pulsed noise cannot be quickly canceled out, making stable tracking impossible. Therefore, if the time constant of the high-pass filter 12 is switched to a small value, the charge corresponding to the above-mentioned extra energy will be accumulated in the capacitor, and since this charge will be quickly discharged, the high-pass error signal will contain the above-mentioned pulse. A pulse of opposite polarity is generated that quickly cancels out the sexual noise. FIG. 4 <c> shows the high-frequency error signal at this time, which is added to the low-frequency error signal shown in FIG. 4(d), and a control signal as shown in FIG. applied. As a result, the above-mentioned extra energy is quickly canceled out, and tracking becomes stable.

As explained above, according to the present invention, stable tracking can be performed even with respect to defects in the information recording carrier.

In the above description, the defect detection means is not particularly limited. For example, the defect detection means may be envelope-detected to detect a drop in the amplitude of the reproduced signal, or if the interval between zero crosses of the reproduced signal is longer than a predetermined length. It may also be possible to detect that the length of Furthermore, the method of detecting the tracking error is not particularly limited; for example, the information signal detector may be divided into two parts and the levels of the respective detection signals may be compared, or in the case of an optical information reproducing device, , an imbalance in the light amount distribution of reflected light from the information recording carrier caused by tracking error may be detected. Furthermore, the reproducing head is not particularly limited, and may be one that reads information optically, or may be a so-called magnetic head. Furthermore, there are no particular limitations on the above-mentioned changeover switch or high-pass filter, and there are no particular limitations on the configuration of the low-pass filter as long as the time constant and order are set so that its output hardly responds to the above-mentioned pulsed noise. Not done. For example, these can be configured as shown in FIG. FIG. 5 is a circuit diagram of the main parts of a tracking control device in an embodiment of the present invention, in which 21 is a first operational amplifier, 22 is a second operational amplifier, and 23 is a third operational amplifier.
24 is an analog switch.

Terminals B, C, D and E correspond to points B, C, D and E in FIG. 3, respectively. In the same figure, resistance R,,
R2, R5, capacitors CI, C2, and second operational amplifier 22 constitute a low-pass filter, and resistor R3 or resistor R4 and capacitor C3 constitute a high-pass filter. However, in this case, the high-frequency error signal and the low-frequency error signal become currents flowing through the 0 point and the D point, respectively. The first operational amplifier 21 acts as a buffer, and the third
The operational amplifier 23 and the resistor R6 constitute an adding means for adding the low-frequency error signal and the high-frequency error signal, and output the added signal as a voltage. The analog switch 24 switches the time constant of the high-pass filter from R3C5 to R4C5 in accordance with the defect detection signal input from the terminal B, and also switches the input signal. Since these operations have already been explained in FIG. 2, they will be omitted here. Note that the low-pass error signal must not have a large phase delay with respect to the rotational frequency component caused by the eccentricity of the information recording carrier, so the cutoff frequency (172 m) of the low-pass filter is set at a value that is lower than the rotational frequency. 1
It is desirable to set it higher than about 0 constant. If the time constant R3C5 of the high-pass filter is set to be the same as that of the low-pass filter, and R3 and R5 are set to the same value, normally the low-pass filter and high-pass filter can be connected in parallel, and the overall almost flat frequency characteristics can be obtained.

Furthermore, if the cutoff frequency of the low-pass filter is close to the rotational frequency of the information recording carrier, if the gain of the low-pass filter at this rotational frequency is sufficiently larger than the gain of the high-pass filter, the error signal will be reduced. Since most of the rotational frequency components pass through the low-pass filter, the above-mentioned phase delay can be made sufficiently small (see Japanese Patent Application No. 57-1 for details).
(See No. 85663). The gain ratio between the low-pass filter and the high-pass filter at the rotation frequency fr is approximately 2πR6C5/fr when the cutoff frequency of the low-pass filter is greater than fr, so it is desirable to set this to about 10 or more. .

In this case, when the low-pass filter and high-pass filter are connected in parallel, the overall frequency characteristic will generally not be flat, and if R3>R5, low-frequency compensation will be applied.

Effects of the Invention As is clear from the above explanation, the present invention provides tracking control for an information reproducing device, in which a part of the closed loop is
It includes a low-pass filter and a high-pass filter whose pass band has a gain of 1, which are connected in parallel, and when a defect is detected in the reproduction section of the information recording carrier, the output signal of the low-pass filter is transmitted to the high-pass filter. In addition to switching the input of the high-pass filter so that the input is input to Even if a speed error occurs in the actuator due to noise mixed into the control signal just before the detection, this speed error can be quickly canceled out immediately after detection, so tracking control is less likely to be disturbed by defects in the information recording carrier and is stable. You can get the effect of becoming.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a tracking control means in a conventional information reproducing device, FIG. 2 is a signal waveform diagram of each part of the conventional tracking control means, and FIG. 3 is a block diagram of a tracking control means in an embodiment of the present invention. 4 is a signal waveform diagram of each part of the tracking control means in the embodiment of the present invention, and FIG. 5 is a circuit diagram of the main parts of the tracking control means in the above embodiment. ■... Information recording carrier, 2... Reproduction head, 4... Defect detection means, 5... Error detection circuit, 8... Changeover switch, 9...
... Drive circuit, 10 ... Actuator, 1
1...Low pass filter, 12...High pass filter, 13...Adder, 21.22
．． 23... operational amplifier, 24... analog switch. Name of agent: Patent attorney Toshio Nakao Haga 1 person 1
4- Figure 1 Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] an information reading means for reading information from an information recording carrier on which information is recorded on concentric or spiral information tracks; an error detection means for detecting a positional error of an information reading position by the information reading means with respect to the information track; tracking control means including a closed loop for correcting the information reading position according to an error signal output from the error detection means; and a tracking control means that detects a defect in the information recording carrier so that the information reading position almost passes through the defect. has a defect detection means that outputs a defect detection signal when
The tracking control means includes a high-pass filter that passes the high-frequency component of the error signal to obtain a high-frequency error signal, and the gain of the passband is 1 and is connected substantially in parallel with the high-pass filter; a low-pass filter for passing the low-pass component of the error signal to obtain a low-pass error signal; an adding means for adding the low-pass error signal and the high-pass error signal again; and a changeover switch for switching the output signal of the low-pass filter to be input to the band-pass filter, and the high-pass filter is configured to have a time constant switched to a small value in response to the defect detection signal. An information reproducing device characterized by: