Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1998-11-16
2001-01-09
Hindi, Nabil (Department: 2753)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S059160
Reexamination Certificate
active
06172954
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an asymmetry compensation apparatus for applying asymmetry compensation to a reproduced signal, provided, for example, for a reproduction apparatus for disc-shaped recording media.
2. Description of the Related Art
Conventionally, a so-called asymmetry phenomenon is generated in recording pits (“recording pits” here refer to recording marks formed by magneto-optical recording and phase-change recording as well as physically formed holes as in a compact disc (CD)) formed on a disc-shaped recording medium (hereinafter just called a disc) due to changes in various conditions during recording. This asymmetry adversely affects reproduced data so as to generate an error in the length of each inverted period, and may cause inappropriate data reproduction processing.
Therefore, for compensating for such asymmetry, there has been known an asymmetry compensation circuit shown in FIG.
17
.
The asymmetry compensation circuit shown in the figure compensates for asymmetry while it makes an analog reproduced RF signal read from a disc to a binary RF signal (EFM signal in a CD system).
The reproduced RF signal is input to an non-inverted input terminal of a comparator
50
through a coupling capacitor C
10
. A voltage division point at which a DC power source line voltage is divided by resistors R
20
and R
21
is also connected to the non-inverted input terminal of the comparator
50
.
The comparator
50
compares the level of the reproduced RF signal input to the non-inverted input terminal with a threshold TH input to an inverted input terminal of the comparator to generate and output the binary RF signal. This binary RF signal is sent to a required decoding processing circuit system at the subsequent stage. The binary RF signal also branches to be input to a filter section
51
for asymmetry compensation.
The filter section
51
serves as a low-pass filter (integrator) and provided with a first stage filter formed of a resistor R
22
and a capacitor C
11
and a second filter formed of a resistor R
23
and a capacitor C
12
. The filter section
51
has the certain time constant determined by the resistances and the capacitances of these elements.
The filter section
51
filters the input binary RF signal and sends it to an amplifier
52
. If asymmetry causes an error (dispersion) in the length of the inverted period of the binary RF signal, the filter section
51
outputs the DC component having the level corresponding to this error.
Since the output of the filter section
51
is input to the inverted input terminal of the comparator
50
through the amplifier
52
as the threshold TH, the threshold TH varies according to the effect of the asymmetry. With this threshold TH being input, the comparator
50
performs a converging operation such that the binary RF signal in which the effect of asymmetry is canceled is output.
In recent years, a disc called a digital versatile disc ROM or a digital video disc ROM (DVD-ROM) has been developed as an optical-disc recording medium suited to multimedia use. There also have been proposed a rewritable recording medium which is compatible with this DVD-ROM and which does not make the configuration of a recording and reproduction apparatus complicated, and a recording and reproduction system therefor.
In such a recording and reproduction system for a rewritable medium, the minimum recording unit of data is specified in a format. For example, as shown in
FIG. 18A
, data is written in units of blocks, which serve as the minimum units of recording data. In the figure, data is continuous in the order of Block (N−1), Block (N), and Block (N+1). To avoid overlap between the last data of the preceding block and the first data of the current block, a link area having the specified size, called a linking section, is provided.
According to such a format, a recording sequence from the start of data recording to the end is completed in units of blocks at the minimum length.
Assume that data is recorded not continuously but by different recording sequences in Block (N−1), Block (N), and Block (N+1) in FIG.
18
A.
In this case, since recording is performed for Block (N−1), Block (N), and Block (N−1) at different chances, each block may be recorded by a different driver. Even if the same driver is used, an error in laser power in recording or an environment change such as a change in the ambient temperature can be considered.
When data recorded on the same disc with different recording conditions such as described above is reproduced, a characteristic difference such as a change in the amplitude level of a reproduced RF signal is generated between blocks.
FIG. 18B
roughly shows a reproduced RF signal obtained by reproducing the data shown in FIG.
18
A. The width W in the up and down directions of the signal indicates its amplitude level. It is understood from the figure that the amplitude level of a reproduced RF signal may change between blocks if Block (N−1), Block (N), and Block (N+1) are recorded by different recording sequences.
When the asymmetry compensation circuit having the configuration shown in
FIG. 17
is applied to a system in which data is substantially sequentially recorded in a medium, such as a CD system, there occurs no problem if the time constant of the filter section
51
is fixed. On the other hand, if the asymmetry compensation circuit having the configuration shown in
FIG. 17
is applied to a case in which the reproduction state shown in
FIG. 18B
is generated, although the ideal threshold TH should be as shown by a solid line in
FIG. 18B
, since the filter section
51
has a fixed time constant, the threshold level actually does not respond such swiftly and changes to the threshold level TH appropriate for Block (N) with some time difference as shown by a dotted line “a” when reproduction proceeds from Block (N−1) to Block (N). In this case, a binary RF signal for which appropriate asymmetry compensation is not performed is output during the period indicated by the dotted line “a.” This means that reliability of read data deteriorates accordingly.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to improve data-reproduction reliability by applying asymmetry compensation to a reproduced signal read from a disc, namely, by always using an appropriate threshold for producing a binary signal.
The above object is achieved in one aspect of the present invention through the provision of an asymmetry compensation apparatus including: input level detecting means for making a detection signal obtained by comparing the level of a reproduced signal read from a disc-shaped recording medium with a threshold to a binary signal and for outputting the binary signal as a reproduced data signal; asymmetry compensation means provided with a low-pass filter to which the detection signal is input from the input level detecting means, for compensating for asymmetry generated in the reproduced data signal by inputting as the threshold the output of the low-pass filter to the input level detecting means; signal state detecting means for detecting a state in which the state of the reproduced signal matches the specified condition; and time constant changing means for controlling such that the time constant of the low-pass filter is changed at the specified timing when the signal state detecting means detects a state in which the state of the reproduced data signal matches the specified condition.
In the asymmetry compensation apparatus, the time constant changing means may change the time constant of the low-pass filter according to a change in the state of the reproduced signal detected by the signal state detecting means such that the threshold changes so as to allow higher speed tracking than in the standard case.
In the asymmetry compensation apparatus, the time constant changing means may change the time constant of the low-pass filter according to a change in the state of the reproduced
Hindi Nabil
Limbach & Limbach L.L.P.
Sony Corporation
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