Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal level detecting using a reference signal
Reexamination Certificate
1999-07-12
2001-11-27
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal level detecting using a reference signal
C369S059130, C369S059190, C369S124050, C369S124150
Reexamination Certificate
active
06324145
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a digital data reproduction apparatus for reproducing a recording medium, such as an optical disk or a magneto-optical disk, on which digital data such as video, sound or text has been recorded.
BACKGROUND ART
Recently, various types of digital data reproduction apparatuses have been suggested for reproducing a recording medium, such as an optical disk, a magneto-optical disk or a magnetic tape, on which digital data such as video, sound or text has been recorded.
An exemplary conventional digital data reproduction apparatus will now be described with reference to the drawings.
FIG. 23
is a block diagram of a conventional digital data reproduction apparatus outputting reproduced data.
In
FIG. 23
, reference numeral
101
denotes an optical disk on which digital data such as video, sound or text data has been recorded. Reference numeral
102
denotes a pick up which is used as a detector for reading data on the optical disk
101
, and includes an actuator provided therein. Reference numeral
103
denotes waveform equalization means for performing a waveform equalization operation on a signal DRF, which has been obtained by reading data from the optical disk
101
with the pick up
102
, so as to produce an equalized reproduced signal RRF. Reference numeral
104
denotes error signal production means for performing an arithmetic operation on the signal DRF obtained by the pick up
102
so as to produce an error signal ERS which is required for a control operation, and for performing a fine adjustment of the error signals ERS using a jitter detection signal JTR from jitter detection means
108
. Reference numeral
105
denotes control means for controlling focusing, tracking, traversing, or the like, of the pick up
102
using the error signals ERS.
Reference numeral
106
denotes reproduced signal digitization means for digitizing the reproduced signal RRF, whose waveform has been equalized by the waveform equalization means
103
, by comparing the signal RRF with a reference digitization level. The reproduced signal RRF is digitized by the reproduced signal digitization means
106
and output as reproduced data DDS. Reference numeral
107
denotes synchronization means for producing a clock TSJ whose phase is synchronized with the leading and trailing edges of the digitized signal which has been digitized by the reproduced signal digitization means
106
. Reference numeral
108
denotes jitter detection means for detecting a jitter component contained in the reproduced signal DDS which has been digitized by the reproduced signal digitization means, so as to output the level thereof as the jitter detection signal JTR. The jitter detection method includes the method disclosed in Japanese Laid-Open Patent Publication No. 8-87756.
Now, a correlation representing the variation in the jitter level JTR with respect to the reproduced signal digitization level DSL will be described, along with the operating principle of the synchronization means
107
, with reference to
FIGS. 24 and 2
.
FIG. 24
is a principle diagram showing a characteristic correlation between the reproduced signal digitization level DSL and the jitter level JTR, wherein the waveform on the upper portion of the figure is the reproduced signal RRF which is input to the reproduced signal digitization means
106
, and the waveforms on the lower side of the figure are each an output TSJ to be output from the synchronization means
107
which is obtained by digitizing the reproduced signal RRF with one of the respective levels A, B and C of the reproduced signal digitization level DSL.
FIG. 2
is a characteristic diagram showing a reproduced signal digitization level DSL-to-jitter level JTR characteristic, wherein the horizontal axis represents the reproduced signal digitization level DSL and the vertical axis represents the output JTR of the jitter detection means
108
.
In
FIG. 24
, when the digitization level DSL is set to level A, the clock TSJ produced by the synchronization means
107
becomes a spike-like clock as shown beside the label “For level A” in the lower portion of the figure. Then, DSL=level A holds in the characteristic diagram of FIG.
2
. When the digitization level DSL is set to level B of
FIG. 23
, the clock TSJ produced by the synchronization means
107
becomes a pulse-like clock as shown beside the label “For level B” in the lower portion of the figure which has a time width TAB in proportion to the difference between levels A and B. Then, DSL=level B holds in the characteristic diagram of
FIG. 2
, and the jitter JTR is increased from that for level A. Similarly, when the digitization level DSL is set to level C of
FIG. 24
, the clock TSJ produced by the synchronization means
107
becomes a pulse-like clock as shown beside the label “For level C” in the lower portion of the figure which has a time width in proportion to the difference between levels A and C. Then, DSL=level C holds in the characteristic diagram of
FIG. 2
, and the level of jitter is increased from that for level A as in the case of level B. Thus, the level of jitter increases/decreases depending upon changes in the reproduced signal digitization level DSL.
There is an apparatus for adaptively setting the reproduced signal digitization level using as a reference the aperture ratio of the eye pattern of the reproduced signal for the purpose of optimizing the reproduced signal digitization level of such a digital data reproduction apparatus. This apparatus determines the level using a ROM table which has been previously set according to the aperture ratio of the eye pattern of the reproduced signal, and performs a digitization operation on the reproduced signal using the determined level (Japanese Laid-Open Patent Publication No. 5-6619, etc.).
However, the conventional digital data reproduction apparatuses have the following problems:
(1) The reproduced signal digitization level cannot be corrected until a signal is actually reproduced;
(2) The reproduced signal digitization level may not be adjusted so as to minimize the jitter which may cause an error in reading the reproduced signal;
(3) The jitter detection sensitivity in detecting a jitter component contained in a reproduced signal varies among various circuits; and
(4) The individual difference becomes large among circuits for setting the cut-off frequency for waveform equalization of the reproduced signal.
The present invention has been made to solve the above-described problems and has an objective of providing a digital data reproduction apparatus and a method for correcting a reproduced signal digitization level in which the quality of the reproduced signal from the recording medium is kept high while ensuring the reproduction stability.
DISCLOSURE OF THE INVENTION
A digital data reproduction apparatus of the present invention comprises: reproduced signal digitization means for digitizing a reproduced signal; synchronization means for producing a clock whose phase is synchronized with a leading edge and a trailing edge of the digitized signal produced by the reproduced signal digitization means; and jitter detection means for integrating and thereby converting absolute values of phase errors between the digitized signal and the clock to a voltage value, the apparatus further comprising digitization level correction means for correcting a reproduced signal digitization level so as to minimize a signal produced by the jitter detection means, thereby achieving the above-described object.
The digital data reproduction apparatus may further comprise: pseudo reproduced signal production means for producing a pseudo reproduced signal; and a switch for switching a signal to be sent to the reproduced signal digitization means by selecting one of the signal produced by the pseudo reproduced signal production means and a normal reproduced signal.
A method for correcting a reproduced signal digitization level of the present invention comprises the steps of: obtaining a first proportional function within a p
Edahiro Yasuaki
Horibe Ryusuke
Kobayashi Motoyuki
Matsumoto Yasuki
Matsushita Electric Industrial Co. Ltd
Renner , Otto, Boisselle & Sklar, LLP
Tran Thang V.
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