JP2001006181A - Apparatus for measuring jitter of optical disc - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure jitter accurately by detecting a large volume of effective data for use in statistic processing in a short time. SOLUTION: The jitter measuring apparatus 1 comprises an OP 3 and a preamplifier 4 for reproducing an RF signal from an optical disc 2, a binarization circuit 5 for the RF signal, a memory 6 for storing the binarized data, and a CPU 7. The CPU 7 measures the time width from an arbitrary edge of a binarized data to an edge of the optical disc 2 separated by 12T or more and processes a plurality of measured time widths statistically thus measuring jitter of a data reproduced from the optical disc 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting the specifications and characteristics of an optical disk, and more particularly to an apparatus for measuring the jitter of data reproduced from an optical disk.

[0002]

2. Description of the Related Art Conventionally, at the time of manufacturing, shipping, or product development of an optical disk such as a CD, it has been inspected whether the manufactured optical disk satisfies specifications. In the specification of the optical disc, there is generally an item of jitter of the reproduced data, and in the inspection of this item, the measurement of the jitter is performed.

[0003] Data reproduced from an optical disk is obtained by binarizing an RF signal reproduced by an optical pickup. Each of the binarized data normally has a cycle that is an integral multiple of the cycle (T) of the reproduction clock. For example, in the case of a compact disc, data from 3T to 11T is reproduced. However, due to the influence of manufacturing errors, pickup characteristics, and the like, the period of each reproduced data has a temporal fluctuation. In other words, even if the data originally has a time width of, for example, 5T, the data will not be exactly data having a period of 5T, but will be data having a period of 5.3T or 4.9T, for example. Such temporal fluctuation when the RF signal of the optical disc is binarized is called jitter of the reproduction data of the optical disc.

[0004] As a method of inspecting the jitter of an optical disc,
An evaluation method generally called a 22T method is used. This 22T method is a method that uses 22T ± 0.5 from a certain edge.
The measurement is performed by measuring a time width up to an edge existing in the range of T and obtaining a standard deviation when statistically processing a plurality of measured time widths. This 22T method is used because it has a good correlation with the block error rate.

[0005] Specifically, in the 22T system, as shown in FIG.
A window is opened between 1.5T and 22.5T. Then, an edge is detected between 21.5 and 22.5T. If there is an edge in the window, measure the time width. For example, assuming that the edge t1 exists in the window, the time width T1 from the edge t0 to the edge t1 is measured.

Then, the next measurement is started. For example, counting starts from the edge t1, and from the edge t1 to 21.
Open the window between 5T and 22.5T. If there are no edges between the windows, no time measurement is taken. For example, the time width from edge t1 to edge t2 is
If it is 23T, there are no edges in the window. Then, after closing the window where this time measurement was not performed, counting starts again from the next first edge,
The window is opened again between 21.5T and 22.5T to detect an edge.

In the 22T system, generation of a window, detection of an edge, and measurement of a time width are repeated as described above.
The measurement of the time width related to T is performed several times. Then, statistical processing is performed from the measurement data having a plurality of time widths to determine the jitter of the reproduction data of the optical disk.

[0008]

By the way, the above-mentioned 2
In the 2T method, only data having a period of 22T (± 0.5T) is used for jitter measurement.
If no edge exists in the period of 0.5T), no measurement is performed.

For example, assuming that an edge appears at a random probability during 22T (± 0.5T), if the expected value of the period of the reproduced data is 3T, the appearance probability of the edge is 1 /.
It becomes 3. Actually, since there are a lot of data having a period longer than 3T, the appearance probability of the edge during 22T (± 0.5T) is 30% or less. That is,
Only one valid data can be obtained with a period of 66T or more.

Therefore, in the conventional 22T system, much time is spent for measuring data used for statistical processing.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and it is an object of the present invention to provide an optical disc jitter measuring apparatus for detecting valid data used for statistical processing in a short time and measuring jitter with high accuracy. Aim.

[0012]

In order to solve the above-mentioned problems, a jitter measuring apparatus according to the present invention comprises a reproducing means for reproducing an RF signal from an optical disk, and a binarizing means for binarizing the RF signal. Storage means for storing data binarized by the binarization means; and jitter measurement means for measuring jitter of reproduction data of the optical disk based on the data stored in the storage means. The measuring means measures a time width from an arbitrary edge of the data binarized by the binarizing means to an edge separated from the maximum pit length or the maximum land length of the optical disc, and calculates a plurality of measured time widths. Statistical processing is performed to measure the jitter of the reproduction data of the optical disk.

In this optical disc jitter measuring apparatus, the time width from an arbitrary edge of the data binarized by the binarizing means to an edge separated from the maximum pit length or the maximum land length of the optical disk is measured. Statistical processing is performed on the plurality of measured time widths to measure the jitter of the reproduction data of the optical disk.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a jitter measuring apparatus according to an embodiment of the present invention.

The jitter measuring device 1 shown in FIG.
This is a device for measuring the jitter of the optical disk 2 (so-called compact disk) on which a 1T signal is recorded.

The jitter measuring apparatus 1 includes an optical pickup 3 for detecting a signal recorded on an optical disk 2, a preamplifier 4 for generating a reproduction signal (RF signal) from a detection signal from the optical pickup 3, and Value 2
It comprises a value conversion circuit 5, a memory 6 for storing the binarized data in time series, and a CPU 7 for measuring jitter from the data stored in the memory 6.

Next, a method of measuring jitter by the jitter measuring apparatus 1 will be described.

On the memory 6, the binarized data is stored in a time series, and the rising edge and the falling edge of each data are stored corresponding to the reproduction time. For example, assume that binarized data is stored as shown in FIG.

The CPU 7 reads out the data stored in the memory 6 and, from a certain edge (starting edge),
The first edge (corresponding edge) among the edges existing between 9.5T and 31.5T is detected, and the time width between the start edge and the corresponding edge is measured. That is, the window is opened when 19.5T has elapsed from the start edge, and the window is closed at 31.5T. Then, an edge that first exists temporally in this window is detected, and this is set as a corresponding edge. For example, when the edge t0 shown in FIG.
The edge t3 existing at the position from 0 to 22T is the corresponding edge, and the time T1 between t0 and t3 is measured.

Subsequently, the first edge (corresponding edge) of the edges existing between 19.5T and 31.5T is similarly detected with respect to the edge next to a certain edge measured last time. The time width between the start edge and the corresponding edge is measured. For example, the same measurement is performed for t1 shown in FIG. When the edge t1 is set as a start edge, an edge t4 existing at a position 24T from the edge t1 becomes a corresponding edge, and a time T2 between the t1 and t4 is measured.

This is performed for all edges. For example, the time is also measured for t2 to t11 (or all edges longer than that shown in FIG. 2).

As described above, by measuring the time width for all the edges, the data of the time width for performing the statistical processing increases.

The start edge may be only the rising edge or only the falling edge.

Here, the window is opened when 19.5T has elapsed from the start edge, and the window is closed at 31.5T, that is, the edge whose period from the start edge is 20T to 31T is detected. For the following reasons.

When measuring the jitter, it is not preferable to use the information of the same pit or the edge between the same lands, since the influence of the manufacturing process is greatly affected. For example, using the time width between the edges of the different lands as shown in FIG. 3B rather than using the time width between the starting edge and the ending edge of the same land as shown in FIG. Low process impact. Therefore, the length from the start edge to the start of the window is set to be longer than the maximum pit length or the maximum land length of the optical disk to be measured. For compact discs, the maximum pit length is 11T
(Frame sync), the jitter measuring apparatus sets the time to 12T or more.

In a compact disk, two consecutive 11T data are recorded as a frame sync. For other data, the maximum cycle from one pit to the next pit is 20 (10T + 10).
T) is the maximum period. Since the period of 20T is close to 22T which has a good correlation with the block error rate, it is possible to detect jitter with high accuracy. When the time from the start edge to the opening of the window is 20T, if the end position of the window is 31T obtained by adding 11T to 20T, one edge is always included in the window.

As described above, by opening the window when 19.5T has elapsed from the start edge and closing the window at 31.5T, jitter can be measured for all edges.

Then, statistical processing is performed on the plurality of jitters measured in this way to determine the amount of jitter in the data reproduced from the optical disk.

As described above, the jitter measuring apparatus 1 according to the embodiment of the present invention can measure a large amount of data used for statistical processing in a short time. For this reason, even when the jitter cannot be measured for all data recorded on the optical disc due to a limitation of a memory, an arithmetic unit, and the like, the jitter can be efficiently measured in the limited reproduction data. . In addition, the start position of the window is set to 19.
With 5T, the jitter can be measured efficiently and accurately.

Here, the number of valid data in the conventional 22T system is compared with the number of valid data measured by the jitter measuring apparatus 1.

First, let a be the probability that an edge exists within 1T time.

In the conventional 22T system, valid data is obtained only when there is an edge while the 1T window is open, so that one valid data can be obtained at a period of (22 / a) T. For example, if a = 0.33 (33%), one valid data can be detected at 66T.

On the other hand, in the jitter measuring apparatus 1 described above,
Since all edges are valid data, one valid data can be detected only by the reciprocal of the edge existence probability, that is, in a period of (1 / a) T.

Thus, in the jitter measuring apparatus 1, when the time width is measured using both the rising edge and the falling edge, it is possible to obtain effective data 22 times as large as the conventional 22T method.

[0036]

In the optical disk jitter measuring apparatus according to the present invention, the time width from an arbitrary edge of the data binarized by the binarizing means to an edge separated from the maximum pit length or the maximum land length of the optical disk. Is measured, and a plurality of measured time widths are statistically processed to measure the jitter of the reproduction data of the optical disc. Therefore, a large amount of valid data used for the statistical processing is detected in a short time, and the jitter is measured with high accuracy. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram of a jitter measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating the content of a jitter measurement process performed by the jitter measurement device.

FIG. 3 is a diagram illustrating a detection position of reproduction data of the jitter measuring apparatus.

FIG. 4 is a diagram for explaining the measurement processing when jitter is measured by a conventional 22T method.

[Explanation of symbols]

1 jitter measuring device, 2 optical disk, 3 preamplifier, 4 binarization circuit, 5 memory, 7 CPU

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Claims (3)

[Claims] A reproducing means for reproducing an RF signal from an optical disk; a binarizing means for binarizing the RF signal; a storing means for storing data binarized by the binarizing means; Jitter measuring means for measuring the jitter of the reproduction data of the optical disk based on the data stored in the means, wherein the jitter measuring means calculates the jitter from an arbitrary edge of the data binarized by the binarizing means. Measuring the time width of the optical disk up to the edge distant from the maximum pit length or the maximum land length, performing statistical processing on the plurality of measured time widths, and measuring the jitter of the reproduction data of the optical disk; Jitter measurement device. 2. The optical disc, wherein a clock cycle of reproduced data is T and data from 3T to 11T is recorded, and the jitter measuring means is at least 12T from an arbitrary edge of the binarized data. At a distant point, a window of a predetermined time width for edge detection is opened, a time width from this arbitrary edge to an edge existing in this window is measured, and a jitter of reproduction data of the optical disc is measured. The optical disc jitter measuring apparatus according to claim 1, wherein: 3. The jitter measuring means opens a window having a time width of 12 T or less for edge detection at a point 12 T or more away from an arbitrary edge of the binarized data, and starts the window within the window from the arbitrary edge. 3. The optical disc jitter measuring apparatus according to claim 2, wherein a time width up to a first edge existing in the optical disc is measured to measure a jitter of reproduction data of the optical disc.