JPH01300480A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To prevent a noise spectrum from being folded in a control area by setting a sampling frequency between the noise spectra of a reproducing information signal included in a position error signal. CONSTITUTION:To sample the position error signal 7a at a position error sampling means 8 with a frequency having relation of non-integer times with the frequency of a reproducing synchronizing signal 3a, the sampling frequency is set between the noise spectra of the reproducing information signal 2a included in the position error signal 7a. Thereby, it is possible to evade the folding of the noise spectrum in the control area, and since the noise spectrum can be eliminated easily by a digital filter, the order of an analog filter can be decreased. Also, it is possible to eliminate or decrease the number of out-fitting components by employing such device.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention divides recorded data into frames or blocks like an optical disk, and adds a synchronization signal to each frame or block to record information on a disk. The present invention relates to an optical information reproducing device for tracking a reproducing head on an information track.

BACKGROUND OF THE INVENTION With recent advances in semiconductor process technology, microprocessors and digital signal processors capable of high-speed calculations have been announced one after another.

The high-speed calculation capabilities of these processors are being used to create a technological trend that is shifting from conventional analog control to digital control in control fields that require high-speed response, such as head positioning.

One of the technical issues to be solved in order to digitally configure such positioning control (ie, control for causing the playback head to follow fluctuations in the information track) is the selection of the sampling rate.

On the other hand, in the optical information reproducing apparatus as described above, the obtained position error signal is mixed with noise resulting from cross-modulation of the reproduced information signal. This noise causes a deterioration in positioning accuracy even in normal analog control, but in a digital control system, it is folded back due to sampling and enters the control band, so it causes a deterioration in positioning accuracy more than in analog control. occurs. Therefore, in order to remove this noise, it is common to insert a low-pass filter using an analog circuit after the error detector to prevent the above-mentioned aliasing phenomenon. (For example, JP-A-62-10243
Problems to be Solved by the Invention However, the analog low-pass filter described above has two problems.
It is necessary to use a high-order low-pass filter of the following order or higher.

On the other hand, if the control method is a general PID controller, the order of this controller is 61\-7 or 1st order. That is, compared to analog control, digital control has the problem that it is necessary to further add a filter of a higher order than the controller that determines the original control accuracy just for noise removal.

In addition, this analog low-pass filter poses a problem in that when the above-mentioned digital control is integrated into an LSI, the external parts of the LSI remain as components, which becomes an obstacle to downsizing and cost reduction of the entire control circuit. There is.

In view of the above problems, the present invention provides an optical information reproducing device that is easy to downsize and inexpensive by reducing the scale of external analog components.

Means for Solving the Problems In order to solve the above problems, the optical information reproducing device of the present invention outputs a reference synchronization signal and a sampling signal having a frequency that is a non-integer multiple of the frequency of the reference synchronization signal. 96, which is optically reproducible, and a synchronization signal for identifying the information divided into predetermined block units and the actual block units;
A disk recorded on qualitatively concentric information tracks;
a playback head which is movable in the radial direction of the disc and obtains a playback signal from the information track; an information playback means which plays back the information signal from the playback signal and extracts a playback synchronization signal; and the reference synchronization signal. disc control means for maintaining a relative scanning speed between the disc and the reproducing head at a constant value so that the frequency of the disc and the reproduction synchronization signal match;
position error detection means for detecting a relative positional error of the playback head with respect to the radial direction of the information track from the playback signal; and position error sampling for sampling the output of the position error detection means in accordance with the sampling signal. a position control means for processing the output of the position error sampling means to obtain an operation signal; and a playback head driving means for correcting the position of the playback head in accordance with the operation signal. It is something that

According to the above-described configuration, the present invention sets the standardization frequency between the noise spectra of the reproduced information signal included in the position error signal, so that this noise spectrum falls within the control band. You will no longer be called back.

This noise spectrum can therefore be easily removed by digital low-pass filtering (so-called digital filtering).

Since the order of the twisted analog low-pass filter can be reduced, external components can be reduced or eliminated.

Example Below, regarding an optical information reproducing device according to an example of the present invention,
This will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the optical information reproducing apparatus of the present invention.

In FIG. 1, numeral 1 is a disk on which encoded information signals are recorded. This information is obtained by combining a certain number of data into one block when creating a disk, and adding a synchronization signal to the beginning of each block to distinguish between blocks.

This information signal is transmitted to the information track 1 formed on the disk 1.
It is recorded in a. In CD format audio information, it refers to a frame synchronization signal (frequency f = 7.35kHz).

The playback head 2 receives a playback signal 2 from this information track 1a.
a is read out and sent to the information reproducing means 3.

This reproduced signal 2a is decoded by the information reproducing means 3, extracts the recorded information, and separates the previously recorded synchronization signal, which is output as a reproduced synchronization signal 3a. This reproduced synchronization signal 3a is phase-compared with the reference synchronization signal 4a output from the reference signal generation means 4 in the disc control means 5, subjected to filtering processing such as phase compensation, and then outputted as a rotation control signal 5a. In response to this rotation control signal 5a, the rotational speed of the disc drive motor 6 changes so that the frequency of the reproduction synchronization signal 3a and the frequency of the reference synchronization signal 4a match.

A series of loops consisting of the disk 1, the reproducing head 2, the information reproducing means 3, the disk control means 5, and the disk drive motor 6 constitute a phase control loop for the disk 1. Through this series of loops, the speed at which the reproducing head 2 scans the information track 1a is controlled to match the speed at which the information was recorded on the disk. Since the above operating principle is already well known, further detailed explanation will be omitted.

On the other hand, the reproduction signal 2a is also sent to a position error detection means 7, which detects a relative position error between the reproduction head 2 and the information track and outputs it as a position error signal 7a. Here, the positional error is a radial error between the information track and the reproducing head, and means a so-called tracking error. A three-beam method, a far-field method, and the like have been proposed as methods for detecting this tracking error, and since all of these methods are well known, detailed explanations thereof will be omitted.

Now, this position error signal is digitized by the position error sampling means 8 and sent to the position control means 9 as position error data 8a. The position control means 9 performs proportional-integral-differential calculation (PID) on this position error data and outputs it as position operation data 9a. The reproducing head driving means 10 converts this position operation data 9a into a current, and corrects the 1o vane position error of the reproducing head 2. A series of loops comprising the reproducing head 2, position error detecting means 7, position error sampling means 8, position controlling means 9, and reproducing head driving means 10 constitute a tracking control loop for the reproducing head 2.

The response frequency (ie, control band fw) of this positioning control loop is generally designed to be 1 kHz or less. For example, in the case of a CD player, fw is designed to be 600 to 8 QO) (z).

Now, in this positioning control loop, the reproduced signal 2a reproduced from the disc 1 has a frequency spectrum as shown in FIG. 2 (-). In FIG. 2(a), these frequency spectra S1. S2. ....

Sn is a spectrum having a frequency that is an integral multiple of the frequency of the reproduction synchronization signal 2a. Here, f1=fo.

f2=2fo, -, fn=nfo, where n represents a natural number and fo represents the frequency of the reproduction synchronization signal.

By the way, when this frequency fn is sampled by the sampling frequency f8, the frequency amount n' of the spectrum of this aliasing noise is fn'=fn(mod f/2)...
・・・・・・・・・(1) It is given by 11 7\-7. Here, A (mod B) represents a remainder group modulo B. For example, if we set f ll = fo (2m+1)/2 (m is a natural number) = (2), the aliasing spectrum of the noise with the lowest frequency will be Sm+1 (frequency (m+1)
)fo) is returned spec)/shi. Therefore, the frequency band of aliasing noise is expressed by equation (1) and (2).
) formula, fn'≧f0/4 (>fw) ・・・・・・・・・
・・・・・・・・・(3) Satisfies the following relationship. for example,
In the case of a CD player, since f0=7350)h, the ratio f'=1837.5 can be set within the range of the control band fW described above.

Therefore, the noise spectrum after sampling can be expressed as shown in FIG. 2(b). This folded spectrum can be easily removed by a digital filter.

FIG. 3 is a block diagram showing an example of the configuration of such a digital filter and its connection relationship.

In FIG. 3, 31 and 32 are delay elements, which are composed of a shift register or a writable memory element (RAM). Also, 33 and 34 are adders, 35.36.3
7 and 38 are coefficient units, for example, a multiplier and a coefficient RO
It is composed of M (read-only storage elements).

A/D converter 30 digitizes position error signal 7a and outputs it to digital filter 8b. The A/D converter 30 and the digital filler 8b constitute the position error sampling means 8 in FIG. This digital filter 8b constitutes a low-pass filter that suppresses the above aliasing noise, and the transfer function F (z) of this digital filter 8b is given by the following equation.

Here, a, b, c, and d are each coefficient multiplier 35.
The values are 36.37 and 38. These values can be easily realized by designing using a model analog filter z-transform13,-.

Ru. The cutoff frequency f of this analog filter. Ha, fw
(f.kuf./4 ・・・・・・・・・・・・・・・
...It should be designed to satisfy (5). Further, as a method for designing a digital filter from an analog filter, bilinear transformation, forward difference approximation, or backward difference approximation may be used. Also, in the above explanation, it was explained as a hardware circuit, but this digital /L/11
The filter may be configured in software on the processor.

FIG. 4 is a block diagram showing another connection relationship of the digital fist filter in the embodiment of FIG. 1.

In FIG. 4, the main control circuit 9b uses position error data 8a.
After performing calculations such as integral compensation and phase compensation, the signal is output to the digital filter 9c. The digital filter 9c is the same as the digital filter 8b in FIG.
Since it is the same as that, it will not be explained repeatedly here. The main control circuit 9b and digital filter 9c described above constitute the position control means 9 in the embodiment of FIG. The reproduction head driving means 10 performs D/A conversion or PWM conversion on the output of the digital filter 9C, and outputs a position correction signal 10a for correcting the position error of the reproduction head. Other operations are the same as those in the embodiment shown in FIG. 1, so detailed explanation will be omitted.

Now, the reference signal generating means 4 can be easily realized using a frequency signal from a single oscillation source.

FIG. 5 is a block diagram showing an example of the configuration of the reference signal generating means 4 in the present invention.

In FIG. 5, the main oscillation source 41 is (2m+1)kfo
The first frequency divider 42 uses this main oscillation frequency signal f. k (2m-1-1)
A reference synchronization signal 4a is generated by dividing the frequency by k, and the second frequency divider 43 uses this main oscillation frequency f. The frequency of k is divided by 2 to generate a sampling signal 4b.

Accordingly, the reference synchronization signal 4a and the sampling signal 4b have a non-integer multiple relationship, and have a single main oscillation frequency signal f.

It is possible to create both signals.

Therefore, a reference synchronization signal and a sampling signal are created15,
, -/ Since it is not necessary to provide an independent oscillation source to achieve this, the cost can be easily reduced.

In this embodiment, the frequency f of the reference synchronization signal. The relationship between f(mOdfo)〆0 and the frequency of the sampled signal f6 is assumed to be (2m+1): 2, but this relationship may also be (2m+1): 3, and more generally, if the relationship f(mOdfo)〆0 holds. , a similar effect can be obtained.

Furthermore, in the above explanation, an example was described in which no aliasing prevention filter is provided before the position error sampling means, but for example, when low-level white noise is mixed, fB/
In order to remove two or more of these white noises, a simple approximately first-order analog low-pass filter may be inserted before the A/D converter constituting the position error sampling means.

In addition, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without changing the gist.

Effects of the Invention As described above, according to the present invention, since the position error signal is sampled at a frequency that is a non-integer multiple of the frequency of the reproduction synchronization signal, the noise spectrum of the reproduction information signal included in the position error signal is Since the sampling frequency is set in between, this noise spectrum will not be folded back into the control band. Therefore, this noise spectrum is
Since it can be easily removed by fill, it has the advantage that the order of analog fill can be reduced.

In addition, in conjunction with this, the number of external parts can be reduced or reduced.

Therefore, the external device has the excellent effect of making it possible to construct an optical information reproducing device that is easily miniaturized and inexpensive by reducing the scale of analog components.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical information reproducing device according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing a noise spectrum included in a reproduced signal, and FIG. 3 is an embodiment of the embodiment of FIG. FIG. 4 is a block diagram showing another connection relationship of the digital fill, and FIG. 6 shows an example of the configuration of the reference signal generating means. It is a block diagram. 1...disc, 2...playback head, 3.
... Information reproducing means, 4 ... Reference signal generation means, 6 ... Disc control means, 7 ... Position error detection means, 8 ...・Position error sampling means,
9...Position control means, 1Q...Reproduction head drive means.

Claims (5)

[Claims] (1) A reference signal generation means for outputting a reference synchronization signal and a sampling signal having a frequency that is a non-integer multiple of the frequency of the reference synchronization signal, information divided into predetermined block units, and identifying this block unit. a disk on which a synchronization signal for the purpose of recording is recorded on an optically reproducible substantially concentric information track; and a playback head that is movable in the radial direction of the disk and obtains a playback signal from the information track. and,
information reproducing means for reproducing an information signal from the reproduction signal and extracting a reproduction synchronization signal; disk control means for keeping the scanning speed at a constant value; position error detection means for detecting a relative positional error of the reproducing head in the radial direction of the information track from the reproduction signal; a position error sampling means for sampling in accordance with a sampling signal; a position control means for processing the output of the position error sampling means to obtain an operation signal; and a position control means for controlling the position of the playback head in accordance with the operation signal. What is claimed is: 1. An optical information reproducing apparatus comprising: a reproducing head driving means for correcting the information. (2) The optical information reproducing apparatus according to claim 1, wherein the position error sampling means includes means for digitizing the position error signal. (3) The optical information reproducing apparatus according to claim 2, wherein the position error sampling means includes means for smoothing the position error data by numerical calculation. (4) The optical information reproducing apparatus according to claim 2, wherein the position control means includes means for smoothing the operation signal by numerical calculation. (5) The reference signal generation means includes an oscillation source that outputs a main frequency signal having a frequency that has a relationship of an integral multiple of the least common multiple of the frequency of the reference synchronization signal and the frequency of the sampling signal,
2. The optical information reproducing apparatus according to claim 1, wherein the reference synchronization signal and the sampling signal are obtained by dividing a main frequency signal from the oscillation source.