JPH087959B2 - Optical information reproducing device - Google Patents

Description

The present invention relates to a disc on which information is recorded by dividing recording data for each frame or block and adding a synchronization signal for each frame or block like an optical disc. The present invention relates to an optical information reproducing device for tracking a reproducing head on an information track.

Conventional technology With recent advances in semiconductor process technology, microprocessors and digital signal
The announcement of processors is one after another. Utilizing the high-speed computing capability of these processors, we are creating a flow of technology that shifts from conventional analog control to digital control in the control field that requires high-speed response such as head positioning.

One of the technical problems to be solved in order to digitally configure such positioning control (that is, control for making the reproducing head follow the fluctuation of the information track) is selection of the sampling rate.

On the other hand, in the optical information reproducing device as described above,
The resulting position error signal is mixed with noise that is the intermodulation of the reproduction information signal. This noise causes deterioration of the positioning accuracy even in the normal analog control, but in the digital control system, the noise is returned by sampling and enters the control band, so that the positioning accuracy deteriorates more than the analog control. . Therefore, in order to remove this noise, it is common to insert a low-pass filter formed by an analog circuit in the subsequent stage of the error detector to prevent the above-mentioned folding phenomenon. (For example, JP-A-62-102431) Problems to be Solved by the Invention However, the above analog low-pass filter is
It is necessary to use a high-order low-pass filter of second order or higher.

On the other hand, when the control method is a general proportional / integral / derivative controller (PID controller), the order of this controller is 0th order or 1st order. That is, compared with the analog control, the digital control has a problem in that it is necessary to add a filter of a higher order than the controller that determines the original control accuracy only for removing noise.

In addition, this analog low-pass filter has an L level when the above digital control is integrated into a large-scale integrated circuit (LSI).
Since it remains as an external component of the SI, there is a problem that it becomes an obstacle to downsizing of the entire control circuit and cost reduction.

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

In order to solve the above problems, an optical information reproducing apparatus 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. A reference signal generating means, a disc divided into a predetermined block unit and a disc on which a sync signal for identifying the block unit is recorded on an optically reproducible substantially concentric circular information track; It is possible to move in the radial direction of this disk,
Further, the reproducing head for obtaining a reproduced signal from the information track, the information reproducing means for reproducing the information signal from the reproduced signal to extract the reproduced synchronizing signal, and the frequency of the reference synchronizing signal and the frequency of the reproducing synchronizing signal coincide with each other. Disk control means for keeping the relative scanning speed between the disk and the reproducing head at a constant value, and a position error for detecting a relative position error of the reproducing head with respect to the radial direction of the information track from the reproduction signal. Detection means, position error sampling means for sampling the output of the position error detection means in accordance with the sampling signal, and position control means for calculating the output of the position error sampling means to obtain an operation signal. A reproducing head driving means for correcting the position of the reproducing head according to the operation signal is provided.

Action According to the present invention, since the sampling frequency is set between the noise spectra of the reproduction information signal included in the position error signal, the noise spectrum is not folded back within the control band. Therefore, this noise spectrum can be easily removed by a digital low-pass filter (so-called digital filter).

Also, if you need an analog low pass filter,
Since the order of the analog low-pass filter can be reduced, external components can be reduced or eliminated.

Embodiment An optical information reproducing apparatus according to an embodiment of the present invention will be described below 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, reference numeral 1 is a disk on which an encoded information signal is recorded. As for this information, a certain number of data is collected into one block when a disk is created, and a sync signal for distinguishing this block unit is added to the head of this block unit. This information signal is recorded on the information track 1a formed on the disk 1. In the audio information of the CD format, the frame sync signal (frequency f ₀ = 7.35
KHz).

The reproducing head 2 reproduces the reproduction signal 2a from this information track 1a.
Is read out and sent to the information reproducing means 3. This playback signal 2a
Means to extract the recorded information decoded in the information reproducing means 3 and to separate the prerecorded synchronizing signal,
Output as the reproduction synchronization signal 3a. This playback sync signal 3a
Is compared with the reference synchronizing signal 4a output from the reference signal generating means 4 in the disc control means 5 and subjected to filtering processing such as phase compensation and then output as the rotation control signal 5a. Playback synchronization signal according to this rotation control signal 5a
The rotation speed of the disk drive motor 6 changes so that the frequency of 3a and the frequency of the reference synchronization signal 4a match.

A series of loops including the disk 1, the reproducing head 2, the information reproducing means 3, the disk control means 5 and the disk drive motor 6 constitutes a phase control loop of the disk 1. Through this series of loops, the speed at which the reproducing head 2 scans the information track 1a is controlled so as to match the speed at which the information was recorded on the disk. The above-mentioned operation principle is already known, and therefore a detailed description thereof will be omitted.

On the other hand, the reproduction signal 2a is also sent to the position error detecting means 7, detects a relative position error between the reproducing head 2 and the information track, and is output as a position error signal 7a. Here, this position error is an error in the radial direction between the information track and the reproducing head, and means a so-called tracking error. A three-beam method, a far-field method, or the like has been proposed as a method of detecting this tracking error, and since these methods are all known, detailed description thereof will be omitted.

The 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 / derivative calculation (PID calculation) on this position error data and outputs it as position operation data 9a. The reproducing head drive means 10 is
The position operation data 9a is converted into a current to correct the position error of the reproducing head 2. A series of loops including the reproducing head 2, the position error detecting means 7, the position error sampling means 8, the position control means 9 and the reproducing head driving means 10 constitute a tracking control loop of the reproducing head 2. The response frequency of this positioning control loop (ie control band
fw) is generally designed below 1kHz. For example, for a CD player, fw is designed to be 500Hz to 800Hz.

Now, in this positioning control loop, the inventors have found that the position error signal 7a contains noise having a frequency spectrum as shown in FIG. 2 (a) in addition to the component representing the position error. Confirmed experimentally. Fig. 2 (a)
In, the frequency spectra S ₁ , S ₂ , ..., Sn are spectra having a frequency fn that is an integral multiple of the frequency of the reproduction synchronization signal 2a. Here, f ₁ = f ₀ , f ₂ = 2f ₀ , ..., Fn = nf ₀ , n represents a natural number, and f ₀ represents the frequency of the reproduction synchronization signal.

By the way, if this frequency fn is sampled by the sampling frequency fs, the frequency f of the aliasing noise spectrum f
n'is given by fn '= fn (mod fs / 2) ... (1). Where C = A (mod B) is A = n.
It is defined as representing C in the relationship of B + C. N is 0
Or refers to a natural number. The inventors experimentally found that such a relationship of the equation (1) is established by sampling. Now, as an example, if fs = f ₀ (2m + 1) / 2 (m is a natural number) ... (2) is set, the aliasing spectrum of the noise having the lowest frequency is Sm + 1 (frequency (m + 1) f ₀ ) is aliased. The spectral frequency of the generated noise can be calculated as follows.

The relationship of (m + 1) · fo = 2 · (fo · (2m + 1) / 4) + fo / 2 = 2 · (fs / 2) + fo / 2 is established, and the minimum frequency of aliasing noise is fo from equation (1). It becomes clear that it is / 2.

Therefore, the frequency band of the aliasing noise satisfies the relationship of fn ′ ≧ fo / 2 (3). Here, for example, in a CD player, since fo = 7350 Hz, fn ′ ≧ 3675 Hz> fw (500 to 800 Hz), and as shown in FIG. 2B, aliasing noise is outside the control band fw. Can take the spectrum of.

Therefore, the noise spectrum after this sampling is the second
It can be represented as shown in FIG. This folded spectrum is
It 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 shift registers and writable storage elements (RAM). Further, 33 and 34 are adders, and 35, 36, 37 and 38 are coefficient multipliers, which are composed of, for example, multipliers and coefficient ROMs (read-only memory elements).

The A / D converter 30 digitizes the position error signal 7a and outputs it to the digital filter 8b. The A / D converter 30 and the digital filter 8b constitute the position error sampling means 8 in FIG. This digital filter 8b is
A transfer function F (z) of the digital filter 8b is constructed by forming a low pass filter for suppressing the above-mentioned folding noise.
Is given by the following equation.

Where a, b, c and d are coefficient units 35, 36 and 37, respectively.
And 38 values. These values can be easily realized by designing a model analog filter using z conversion. Cutoff frequency fc of this analog filter
Should be designed so as to satisfy fw <fc <fo / 2 (5). As a method of designing a digital filter from an analog filter, bilinear transformation, forward difference approximation or backward difference approximation may be used. Further, although the above description has been made as a hardware circuit, this digital filter may be configured by software on the processor.

FIG. 4 shows this digital circuit in the embodiment of FIG.
It is a block diagram showing other connection relations of a filter.

In FIG. 4, the main control circuit 9b performs calculation such as integral compensation and phase compensation on the position error data 8a and then outputs it to the digital filter 9c. Digital Falta
9c is identical to the digital filter 8b in FIG. 3 and will not be described again here. The above main control circuit 9b and digital filter 9c are the first
The position control means 9 in the illustrated embodiment is constituted. The reproducing head driving means 10 outputs the output of the digital filter 9c to D /
A conversion or PWM conversion is performed, and a position correction signal 10a for correcting the position error of the reproducing head is output. The other operation is the same as that of the embodiment shown in FIG.

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

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

In FIG. 5, a main oscillation source 41 is a crystal oscillator that oscillates at a frequency of (2m + 1) kf ₀ , and a first frequency divider 42 divides this main oscillation frequency signal fck by (2m + 1) k to obtain a reference. The synchronizing signal 4a is generated, and the second frequency divider 43 divides the main oscillation frequency signal fck by 2k to generate the sampling signal 4b.

As a result, the reference synchronization signal 4a and the sampling signal 4b have a non-integer multiple relationship, and both signals can be generated from a single main oscillation frequency signal fck. Therefore, it is not necessary to provide an independent oscillation source to generate the reference synchronization signal and the sampling signal, so that the cost can be easily reduced.

In the present embodiment, the frequency f ₀ of the reference synchronization signal and the sampling signal
Although the frequency relationship of fs is (2m + 1): 2, this relationship may be (2m + 1): 3, and if the relationship of fs (mod f ₀ ) ≠ 0 holds, the same applies. The effect of can be obtained.

Further, in the above description, the example in which the anti-aliasing filter is not provided before the position error sampling means is described.
For example, fs / 2 when low level white noise is mixed.
In order to remove the above white noise, a simple first-order analog low-pass filter may be inserted before the A / D converter that constitutes 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 departing from the spirit of the invention.

As described above, according to the present invention, since the position error signal is sampled at a frequency having a non-integer multiple relationship with 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 the meantime, this noise spectrum is not folded back within the control band. Therefore, this noise spectrum can be easily removed by a digital filter, and
There is an advantage that the order of the filter can be reduced. Further, along with this, external parts can be reduced or reduced.

Therefore, by suppressing the scale of the external analog component, there is an excellent effect that an optical information reproducing apparatus which is easy to be miniaturized and is inexpensive can be configured.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical information reproducing apparatus in 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 a digital filter in the embodiment of FIG. FIG. 4 is a block diagram showing an example of the configuration and its connection relationship, FIG. 4 is a block diagram showing another connection relationship of the digital filter, and FIG. 5 is a block diagram showing an example of the configuration of the reference signal generating means. 1 ... Disc, 2 ... Playback head, 3 ... Information playback means,
4 ... Reference signal generating means, 5 ... Disc control means, 7 ...
Position error detecting means, 8 ... Position error sampling means, 9 ...
Position control means, 10 ... Playback head driving means.

Claims (5)

[Claims] 1. A reference signal generator for outputting a reference synchronizing signal and a sampling signal having a frequency that is a non-integer multiple of the frequency of the reference synchronizing signal, information divided into predetermined block units, and this block unit. And a disk in which a synchronizing signal for identifying is recorded on an optically reproducible substantially concentric circular information track, and is movable in the radial direction of the disk, and a reproduction signal is obtained from the information track. A reproducing head, an information reproducing means for reproducing an information signal from the reproduced signal to extract a reproducing synchronizing signal, and a disc and the reproducing head so that the frequency of the reference synchronizing signal matches the frequency of the reproducing synchronizing signal. Disk control means for keeping the relative scanning speed between them at a constant value, and a position error for detecting a relative position error of the reproducing head with respect to the radial direction of the information track from the reproducing signal. Knowledge means, position error sampling means for sampling the output of the position error detecting means in accordance with the sampling signal, and position control means for calculating the output of the position error sampling means to obtain an operation signal. An optical information reproducing apparatus comprising: a reproducing head driving unit that corrects the position of the reproducing head according to the operation signal. 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 generating means includes an oscillation source for outputting a main frequency signal having a frequency having a relationship of a frequency of the reference synchronization signal and an integer multiple of the least common multiple of the frequency of the sampling signal, and the reference synchronization signal. The optical information reproducing apparatus according to claim 1, wherein the signal and the sampling signal are obtained by dividing the main frequency signal from the oscillation source.