JPH10125011A - Device and method for inspecting recording/producing characteristics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make uniform an error rate measurement value, enhance inspection reliability, and at the same time improve the tact of an inspection process by providing a low-pass filter that can control both a cut-off frequency and a gain. SOLUTION: A recording signal reproduction circuit in a device for inspecting the error rate of a plurality of rotating storages is formed by a circuit below including a low-pass filter 5. The low-pass filter 5 changes the cut-off frequency and the gain of a frequency band near the cut-off frequency. An error rate measuring means 8 reproduces information recorded in a storage 1 based on a signal that passes through the low-pass filter 5 and compares the reproduction information with recorded information 9 used for recording, thus calculating an error rate. A filter constant control means 11 controls the cut-off frequency and the gain of the low-pass filter 5 so that the measured error rate is within a preset range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for inspecting recording / reproducing characteristics of a recording medium such as an optical recording medium, an optical-magnetic recording medium, and a magnetic recording medium, and more particularly, to a recording medium using a plurality of drives. The present invention relates to an apparatus and a method capable of correcting a machine difference between apparatuses and performing a highly reliable inspection by controlling a noise component of a signal reproducing circuit when measuring an error rate of the apparatus.

[0002]

2. Description of the Related Art Conventionally, in a system for measuring a bit error rate or a byte error rate of a recording medium by using a plurality of recording / reproducing characteristics inspection apparatuses, a recording / reproducing method is used as a method of correcting a machine difference between apparatuses. It has been general to control the erasing power so that the error rate when the same recording medium is measured falls within a certain range. However, as described above, the control of the recording / erasing power alone has variations in the noise components of the reproduction signal systems of a plurality of recording / reproducing devices, and the noise components include fluctuation components. It was difficult to control the value to be constant.

[0003] For this reason, it is difficult or impossible to keep the machine difference between the inspection devices within a desired range.
The reliability of the inspection performed using a plurality of inspection devices has been impaired.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus for testing an error rate using a plurality of recording / reproducing characteristics inspection apparatuses. The purpose of the present invention is to improve the reliability of the inspection by allowing the adjustment to be performed within the specified range.

Another object of the present invention is to make it possible to easily increase the number of inspection apparatuses, thereby improving the takt time of the inspection process.

[0006]

In order to solve the above-mentioned problems, a recording / reproducing characteristic inspection apparatus according to the present invention is a recording / reproducing characteristic inspection apparatus used for an error rate inspection of a rotating recording medium. A low-pass filter capable of changing a cut-off frequency and a gain of a frequency band near the cut-off frequency in a recording signal reproducing circuit of the medium; and a signal recorded on a recording medium based on a signal passed through the low-pass filter. Error rate measuring means for reproducing the information which has been recorded, and comparing the reproduced information with the information used for recording to calculate an error rate. The error rate measuring means controls the error rate so that the measured error rate falls within a preset range. And a filter constant control means for controlling the cutoff frequency and the gain of the bandpass filter.

Further, according to the recording / reproducing characteristic inspection method of the present invention, when inspecting the error rate of a rotating recording medium, a recording signal reproducing circuit of the recording medium reduces a reproduction signal of recording information detected from the recording medium to a low level. Through the band-pass filter, reproduce the information recorded on the recording medium based on the signal passed through the low-pass filter, calculate the error rate by comparing the reproduced information with the information used for recording, Controlling a cutoff frequency and a gain of the low-pass filter so that the calculated error rate falls within a predetermined range to remove or suppress noise components in the reproduced signal. Consists of

In the above apparatus and method, it is preferable that the cut-off frequency fc of the low-pass filter is controlled within the range of fmax ≦ fc ≦ 2fmax with respect to the maximum frequency fmax of the recording / reproducing signal.

The recording medium of the present invention includes:
Although any of an optical recording medium, an optical-magnetic recording medium, and a magnetic recording medium are possible, the present invention is particularly suitable for an optical recording medium.

In the present invention, the measured error rate is stabilized as follows. That is, the error rate depends on the window occupancy of the recording / reproducing signal, and among the reproduction signal jitters that govern the window occupancy, the noise jitter of the reproducing circuit system can be considered as a variable factor.
Therefore, the constant of the low-pass filter is controlled to suppress this noise jitter, the noise component in the high frequency region superimposed on the reproduced signal is controlled, and the digital signal for error rate measurement is obtained from the signal in which the high frequency noise component is controlled. Is obtained. That is, a digital signal is obtained in which jitter fluctuation elements other than the jitter component of the signal reproduced from the recording information recorded on the recording medium are suppressed.

As a result, jitter fluctuation elements are removed or suppressed from the reproduced signal obtained from the recorded information having the same size and interval recorded with the adjusted recording and erasing power, and the error rate measurement value is stabilized.

At this time, if the cut-off frequency fc of the low-pass filter is set to less than 1 in the ratio to the highest frequency fmax of the recording / reproducing signal, the reproducing signal amplitude itself obtained from the recording information decreases and the reproduction signal processing means , The carrier of the signal to be input is reduced, and the S / N tends to decrease. When fc exceeds 2, a noise component in a high frequency range is mixed into the signal. Therefore, in the present invention, fc of the low-pass filter is fmax ≦ fc ≦ 2fm.
It is preferable to set it in the range of ax.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a recording / reproducing characteristic inspection apparatus according to an embodiment of the present invention, and shows a configuration of one of a plurality of inspection apparatuses provided. In the figure, reference numeral 1 denotes a rotating recording medium as an inspection target, for example, an optical recording medium.
Reference numeral 2 denotes a pickup for optically detecting information recorded on the information recording surface of the recording medium 1, for example, scanning the pickup 2 in the radial direction of the recording medium 1 while rotating the recording medium 1. Thus, the recording information of the entire recording area can be read.

The recording information detected by the pickup 2 is as follows:
It is reproduced by the recording signal reproducing circuit. The analog signal detected by the pickup 2 is amplified by the amplifier 3, and the amplified reproduced analog signal 4 is sent to the low-pass filter 5,
It is passed through the filter 5. This low-pass filter 5
Comprises a filter capable of changing and controlling the cutoff frequency and the gain of a frequency band near the cutoff frequency. As the low-pass filter 5, second-order or higher, preferably fourth-order or higher Butterworth characteristics, Chebyshev characteristics,
Alternatively, an analog filter such as a Bessel characteristic can be considered, but a Bessel filter having excellent group delay characteristics is particularly preferable in consideration of characteristics of a signal input to the filter.

The analog signal that has passed through the low-pass filter 5 is binarized by a reproduction signal processing circuit 6 and sent to a computer 10 as a reproduction signal pulse train 7. In the computer 10, an error rate measuring means 8 of a bit error rate or a byte error rate is incorporated as a program. The error rate measuring means 8 compares the recording / reproducing signal (reproducing signal pulse train 7), that is, the reproduction information of the information recorded on the recording medium 1, with the information 9 used for the recording, and calculates the error rate. You. Then, a signal for controlling the cut-off frequency and gain of the low-pass filter 5 is transmitted to the low-pass filter 5 via the filter constant control means 11 so that the measured error rate falls within a preset range. .

In the following, description will be made mainly on the reproducing circuit shown in FIG. First, the fact that the noise jitter and error rate in the reproduction signal detected by the pickup 2 depend on the occupation ratio of the window of the recording / reproduction signal will be described.

As a cause of the deterioration of the reproduced signal, for example, FIG.
As shown in the above, there are the following factors. (1) Reproduction waveform interference: pattern peak shift due to a decrease in resolution of a reproduction signal, crosstalk from an adjacent track, and the like. (2) Waveform distortion: due to the shape distortion of the recording mark, etc. (3) Circuit jitter: group delay distortion, binarized circuit error, P
LL (Phase Locked Loop) phase error and the like. (4) Noise jitter: medium noise, PD (Photo D)
iode) Shot noise, LD (Laser Dio)
de) Noise, head amplifier IV conversion noise, etc. Of these, a part of (1), (2), and (3) is considered to be a peak shift, and becomes a substantially fixed value. Therefore, most of the jitter fluctuation factors are taken as item (4), that is, noise jitter. Can be. Therefore, in the present invention,
This noise jitter is removed or suppressed.

The relationship between the reproduction signal and the reproduction noise will be described. Here, a reproduced signal of an isolated mark (that is, isolated information recorded on a recording medium) is considered. In FIG. 1, when the reproducing circuit using the peak detection method is taken out, FIG.
It becomes as shown in. It is assumed that the reproduction signal F (t) approximates an ideal reproduction signal by a Gaussian function, on which reproduction noise is superimposed.

The reproduction noise v _n (t), the root-mean-square noise power density N (F _n ), and the amplifier output signal V (t) are expressed by Equation 1.

[0020]

(Equation 1)

Here, the output V _D (t) of the differentiating circuit is given by the following equation (2), where the transfer function of the low-pass filter is F (s).

[0022]

(Equation 2)

The zero cross point of h (t) is defined as t _0, and t ₀
Assuming that the gradient of h (t) in the vicinity is G ₀ , G ₀ = d / dt [h (t)] (t = t 0), so that the zero crossing point of V _D (t) can be approximated by Equation 3.

[0024]

(Equation 3)

Here, t ₀ is the above (1), (2),
(3) A fixed value according to the term, and the second term represents jitter due to noise.

Next, in order to simplify the equation, a sine wave g (t) = √2 acos ω ₀ t [a: effective value], and a root-mean-square noise power density N (f _n ) is a fixed value n ₀ ² , Assuming that the low-pass filter is an ideal filter, the mean square value σ ² of the jitter is expressed by Expression 4.

[0027]

(Equation 4)

Therefore, in the recording signal reproducing circuit of the recording / reproducing characteristic inspection apparatus of the present invention, it is understood that the jitter increases as the bandwidth of the low-pass filter increases, that is, as the influence of high-frequency noise increases.

TIA (Time Interval A)
In order to explain the principle of measuring the reproduction noise in the analyzer, the analysis of the reproduction noise is realized by repeatedly measuring a certain time interval on the recording medium. In a certain time interval, the error in the writing process is fixed (included in the peak shift described in the above-mentioned factor of the deterioration of the reproduction signal), and the fluctuation that occurs when the measurement is repeated is caused by the reproduction noise described above. It can be said that it depends.

The standard deviation is used to quantitatively know the variation, and since the time interval includes the variation of the start edge and the variation of the stop edge of the measurement, it is assumed that the respective edges are equally affected by noise. Then, the variation at the edge becomes σ = σ _measure / √2.

In order to explain the concept of the window occupancy, the above-described reproduction noise is considered to be random noise, and therefore, Kε, which gives an error rate of 10 ⁻⁵ from a normal distribution table, is 4.42σ. . Since the window occupation ratio is a proportion of fixed and a varying (sigma) with respect to half the playback window T _w (peak shift) of the window occupation ratio = [4.42 (σ _measure / √2) + peak shift] / (T _w / 2). That is, the relationship is as shown in FIG.

As described above, the error rate depends on the window occupancy, and the window occupancy depends on the reproduction signal jitter. Among the reproduced signal jitters, the variable element is noise jitter as described above. By removing or suppressing this noise jitter, the fluctuation of the window occupancy and, consequently, the error rate can be suppressed.

The removal or suppression of the noise jitter is performed by controlling the cutoff frequency fc and gain of the low-pass filter 5. When the noise jitter is suppressed, only the fixed component is the cause of the deterioration of the reproduced signal, and the fluctuation factor is reduced. Therefore, the machine difference between the inspection apparatuses can be easily corrected by adjusting the recording / erasing power.

That is, from the reproduced signal obtained from the recorded information of the same size and the same interval recorded with the adjusted recording / erasing power, the jitter fluctuation element is suppressed, and a stable result as the measured error rate is obtained. can get.

At this time, by controlling the cut-off frequency fc of the low-pass filter 5 within the range of fmax ≦ fc ≦ 2fmax with respect to the maximum frequency fmax of the recording / reproducing signal, the reproduced signal itself is adversely affected. Noise jitter can be efficiently removed or suppressed. If fc is less than fmax, the amplitude of the reproduction signal decreases, the carrier of the signal input to the reproduction signal processing circuit 6 decreases, and the S / N tends to decrease accordingly. Also,
If fc exceeds 2fmax, noise components in a high frequency range are mixed in, so that noise jitter is increased.

In the present invention, the recording medium is not particularly limited, and includes a phase change optical recording medium, a magneto-optical recording medium, a magnetic recording medium, and the like. The present invention is particularly suitable for high-density recording disks, for example, optical recording media. As an optical recording medium, a medium for writing data using light or an optical property (light reflectance, spectral reflectance,
A write-once or rewritable optical recording medium such as a magneto-optical recording medium that reads data based on a change or a difference in the optical polarization state of the reflected light, or a phase-change optical recording medium is used.

The phase-change type optical recording medium usually has a recording layer provided on a transparent substrate, and a specific metal capable of being reversibly changed between crystal and amorphous by a laser beam is used for the recording layer. ing. The layer configuration on the substrate may be, for example, a layer configuration having at least a first protective layer / recording layer / second protective layer / reflective layer on a transparent substrate.

The recording layer of the phase change type optical recording medium includes, for example, a Te—Ge—Sb—Pd alloy, Te—Ge—Sb—
Pd-Nb alloy, Nb-Ge-Sb-Te alloy, Pt-
Ge-Sb-Te alloy, Ni-Ge-Sb-Te alloy,
Ge-Sb-Te alloy, Co-Ge-Sb-Te alloy,
In-Sb-Te alloys, In-Se alloys, and alloys containing these as main components are used. Especially Te-Ge-
Sb-Pd alloys and Te-Ge-Sb-Pd-Nb alloys are preferable because they hardly deteriorate even when recording / erasing / reproducing is repeated, and have excellent thermal stability. A particularly desirable recording film composition is, for example, in the range represented by the following formula, from the viewpoint of excellent thermal stability and repetition stability. M _z (Sb _x Te _(1-x) ) _1-yz (Ge _0.5 Te _0.5 )
_y 0.35 ≦ x ≦ 0.5 0.20 ≦ y ≦ 0.50 ≦ z ≦ 0.05 where M is at least one metal selected from palladium, niobium, platinum, silver, gold and cobalt, Sb Represents antimony, Te represents tellurium, and Ge represents germanium. Also,
x, y, z and numerals represent the number of atoms of each element (the number of moles of each element). In particular, palladium and niobium preferably contain at least one kind. In this case, z is 0.
It is preferably at least 0005. These alloys are applied on the first protective layer provided on the substrate by, for example, sputtering to form a recording layer.

The first protective layer and the second protective layer mechanically protect the recording layer, and also prevent the substrate and the recording layer from being deformed by heat due to recording and from deteriorating the recording / erasing / reproducing characteristics. In addition, it plays a role in giving the recording layer moisture and heat resistance and oxidation resistance. ZnS,
SiO ₂ , Ta ₂ O ₅ , ITO, ZrC, TiC, Mg
An inorganic film such as F ₂ or a mixed film thereof can be used. In particular, a mixed film of ZnS and SiO ₂ and a mixed film of ZnS and MgF ₂ are excellent in moist heat resistance, and furthermore, are preferable because deterioration of the recording layer at the time of recording / erasing / reproduction is suppressed.

The reflective layer is made of a metal or a mixture of a metal and a metal oxide, a metal nitride, a metal carbide and the like, for example, Zr, Cr, Ta, Mo, Si, Al, Au, P
Metals such as d and Hf, alloys thereof, and mixtures thereof with Zr oxide, Si oxide, Si nitride, Al oxide, and the like can be used. In particular, Al, Au, Ta, alloys thereof, and alloys of Al, Hf, and Pd are preferable because the film can be easily formed.

As a method for forming the first protective layer, the recording layer, the second protective layer, and the reflective layer on the substrate, a method of forming a thin film in a vacuum atmosphere, for example, a sputtering method, a vacuum deposition method, an ion plating method Etc. can be used. In particular, the sputtering method is preferable because the composition and the film thickness can be easily controlled.

As the substrate, it is preferable to use a material through which laser light can be transmitted in order to perform recording and reproduction from the substrate side. For example, polymethyl methacrylate resin,
Organic polymer resins such as polycarbonate resin, polyolefin resin, and epoxy resin, mixtures thereof, copolymers, and glass can be used. Above all, recently, polycarbonate resins have become mainstream.

The substrate is formed into a disk.
The molding method is not particularly limited. For example, injection molding can be used. A stamper having a predetermined groove or male pit formed on the surface is mounted in a mold, and a desired track is formed on the surface by transfer from the stamper. Can be formed.

The size of the substrate needs to conform to the standard required by the optical recording medium drive. For example, it is specified that the substrate is formed into a substrate having a diameter of 90 mm, 120 mm, or 130 mm.

On such a substrate, at least a first protective layer / recording layer / second protective layer / reflective layer are sequentially laminated.
An organic resin protective layer may be further provided on this reflective layer. As the organic resin protective layer, a photocurable resin composition containing a polymerizable monomer or oligomer as a main component or a thermosetting resin composition can be used.

[0046]

As described above, according to the recording / reproducing characteristics inspection apparatus and method of the present invention, the noise jitter in the recording signal reproducing circuit is reduced by using the low-pass filter capable of controlling the cutoff frequency and the gain. In other words, the fluctuation factors in the reproduction circuit can be removed or suppressed in the reproduction circuit, so that the error rate measurement values of multiple recording / reproduction devices can be made uniform, and the dispersion of the inspection data can be managed to be small, and the reliability of the inspection can be maintained. , Reliability can be improved. Also,
Since the variation can be suppressed to be small, it is possible to increase the number of the inspection apparatuses and increase the tact time of the inspection.

Further, it is possible to suppress a reproduction error occurring randomly due to a wide-range noise component of the reproduction system, and to stabilize an error rate measurement value.

[Brief description of the drawings]

FIG. 1 is a block diagram of a recording / reproduction characteristic inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a cause of deterioration of a reproduced signal.

FIG. 3 is a block diagram of a reproduction circuit unit of the apparatus of FIG.

FIG. 4 is a characteristic diagram showing a window occupancy.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Recording medium 2 Pickup 3 Amplifier 4 Reproduction analog signal 5 Low-pass filter 6 Reproduction signal processing circuit 7 Reproduction signal pulse train 8 Error rate measurement means 9 Recording information 10 Computer 11 Filter constant control means

Claims (6)

[Claims] 1. A recording / reproducing characteristic inspecting apparatus used for inspecting an error rate of a rotating recording medium, wherein a cut-off frequency and a gain of a frequency band near the cut-off frequency are provided to a recording signal reproducing circuit of the recording medium in the apparatus. A low-pass filter that can change the information, and reproduces the information recorded on the recording medium based on the signal passed through the low-pass filter, compares the reproduced information with the information used for recording, and outputs an error. Error rate measuring means for calculating a rate, and filter constant control means for controlling the cutoff frequency and the gain of the low-pass filter so that the measured error rate falls within a preset range. A recording / reproducing characteristic inspection apparatus characterized by the above-mentioned. 2. The recording / reproducing characteristic inspection apparatus according to claim 1, wherein a cut-off frequency fc of the low-pass filter satisfies a relation of fmax ≦ fc ≦ 2fmax with respect to a maximum frequency fmax of the recording / reproducing signal. 3. The recording / reproducing characteristic inspection apparatus according to claim 1, wherein the recording medium is an optical recording medium. 4. A method for inspecting an error rate of a rotating recording medium, wherein a recording signal reproducing circuit of the recording medium passes a reproduction signal of recording information detected from the recording medium through a low-pass transmission filter. The information recorded on the recording medium is reproduced based on the signal passed through, and the reproduced information is compared with the information used for recording to calculate an error rate, and the calculated error rate is set in a predetermined range. A method for controlling the cutoff frequency and gain of the low-pass filter so as to remove or suppress noise jitter in the reproduced signal. 5. The recording / reproducing characteristic inspection method according to claim 4, wherein the cut-off frequency fc of the low-pass filter is controlled within a range of fmax ≦ fc ≦ 2fmax with respect to a maximum frequency fmax of the recording / reproducing signal. 6. The method according to claim 4, wherein the recording medium is an optical recording medium.