Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2001-10-29
2004-01-13
Patel, Gautam R. (Department: 2655)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S047210, C369S059160, C714S032000, C375S231000, C360S065000
Reexamination Certificate
active
06678230
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This present invention relates to a technique for equalizing waveform of signals read from recording medium such as optical discs, etc.
2. Description on Related Art
In a information reproducing apparatus for reproducing information recorded on recording medium such as optical discs, a slice method has been adopted, in which a signal waveform level greater than a specified value is judged as “1” and that smaller than a specified value is judged as “0”. However, in this method, it is difficult to reproduce data at a high reliability from the recording medium with remarkably improved recording density. Therefore, in recent years, attention is attracted to Partial Response Maximum Likelihood (hereinafter referred to as PRML) method that can reproduce the data at a high reliability. PRML method is a technique utilized for a signal processing technique of recording medium with increased density, which is utilized in, for example, a digital recording camera integrated type VTR, rewritable optical discs, not to mention a hard disk drive (hereinafter referred to as HDD). As the recording density increases, a need for reproducing data correctly from reproduction signals with low signal-to-noise (S/N) ratio or nonlinear reproduction signals is increased.
FIG. 16
is a block diagram of a general configuration of an information reproducing apparatus
181
using PRML method. First of all, an optical pickup
183
irradiates optical disc
182
with laser beam. Information reproducing apparatus
181
detects intensity of the reflected light, reads the information (data) recorded on optical disc
182
, converts into electrical signals, and outputs to Front End Processor (hereinafter referred to as FEP)
184
. FEP
184
amplifies the electrical signals read and adjusts its gain. FEP
184
further processes to remove noise components of unrequired high frequency band and to emphasize the required signal frequency band. The output signals from FEP
184
are converted to digital signals by analog/digital (A/D) converter
185
and entered into waveform equalizer
186
. Waveform equalizer
186
waveform-equalizes waveforms of the digital signals to the preset PR characteristics. Maximum likelihood decoder
187
decodes waveform-equalized signals to PR characteristics and outputs as the reproduction data.
Waveform equalizer
186
of information reproducing apparatus
181
generates waveform in such a manner as to achieve the desired PR characteristics, that is, PR (3, 4, 4, 3) characteristics.
FIG. 17
is a block diagram of an exemplary configuration of waveform equalizer
186
. Waveform equalizer
186
is called as a transversal filter or Finite Impulse Response (FIR) filter. Waveform equalizer
186
generally includes a plurality of delay elements
192
, a plurality of equalizing coefficients (coefficients A through E) for achieving the desired PR characteristics, a plurality of multipliers
193
for multiplying equalizing coefficients by the output of delay element
192
, and an adder
194
for adding outputs of a plurality of multipliers
193
.
In order to accurately equalize into desired PR characteristics, a technique to automatically adaptively control equalizing coefficients (taps) of FIR filter is adopted. This technique is effective for various stresses such as tilting of a disc, defocus of laser beam, off-track of optical head. Many adaptive control algorithms are known, including Least-mean square (LMS) algorithm, Normalized LMS algorithm, Recursive Least Square (RLS) algorithm, projection algorithm, neural network algorithm.
Now, the adaptive waveform equalizer using LMS algorithm will be briefly described. In this algorithm, a temporary judgment value used for LMS is required in order to calculate adaptive equalizing coefficients. This LMS algorithm utilizes a feedback operation for minimizing square errors between the “desired response” and the “response of transmission line.” This “desired response” is a PR equalization target value. The “response of transmission line” is a digital reproduction signal entered from FIR filter and equalized into PR frequency characteristics. In LMS algorithm, a signal that represents a difference between the temporarily judged value and the digital reproduction signal value after equalization, which is obtained in the block of adaptively controlling the coefficients of FIR filter is called an equalization error signal.
The block that adaptively controls coefficients of FIR filter updates the equalizing coefficients of FIR filter as required to minimize the square value of the equalization error signal. This is called as an adaptive equalization. A formula for setting LMS equalizing coefficients is shown in the following formula (for example, S. Heikin: “Introduction to Adaptive Filters” Gendai Kogakusha):
w
(
n
(
T+
1))=
w
(
nT
)+
A·e
(
nT
)·
x
(
nT
) Eq. (1)
(where, T=0, 1, 2, 3, . . . )
w(nT) represents a present coefficient, w(n(T+1) is a coefficient to be updated, “A” is a tap gain, e(nT) is an equalization error, x(nT) is an input signal to FIR filter. “n” is a parameter for selecting update cycles of the coefficients. Based on Eq. (1) above, the equalizing coefficients of FIR filter is updated.
Now, asymmetry of optical disc
182
(
FIG. 16
) will be described. Asymmetry means absence of symmetry between pits and non-pits of the optical disc. In optical disc
182
(FIG.
16
), information is recorded in the form of arrangement and length of microscopic emboss sections called pits. The pit has length of, for example, 3T, 5T when T denotes the reference length. Pits are arranged with spaces of 3T, 5T. The pit length is preferably exactly 3T, 5T. However, there are some deviations in pit length. This is because a master disc with deviations in pit length is manufactured as a result of, for example, slight deviation of power of recording light used for mastering an optical disc. When the recording power is not appropriate, each pit formed is slightly longer or shorter in the same amount from the standard value in front and behind in the length direction. That is, there is no symmetry between the pits and the non-pits, which is called as asymmetry. Hereinafter, in the present specification, relationships between the pits and the non-pits of the optical disc should be same as the relationships between recorded portions (marks) and unrecorded portions (spaces) of hard disk. Note that, for a read-only optical discs, terms “pit” and “non-pit” may be used and for recordable optical discs, the portion where the information is recorded (that is, portion intensely irradiated with laser) may be called as a “mark” and the region between marks a “space.” In the present specification, terms “pit” and “mark” are synonymous. Terms “non-pit” and “space” and further “non-mark” are synonymous. In addition, a signal when the optical disc with no symmetry between pits and non-pits (that is, asymmetry) is reproduced is called as an asymmetric signal, and a signal when not an asymmetric optical disc is reproduced is called as a symmetric signal.
FIGS. 18A through 18C
show simple models of asymmetry. In
FIGS. 18A through 18C
, 3T marks, 3T spaces, 5T marks, and 5T spaces pit arrangements are shown. In these figures, the reference length is 1T and a detection window width is adopted.
FIG. 18B
is a standard pit arrangement, and both marks and spaces are symmetric. As against
FIG. 18B
,
FIG. 18A
shows marks, each of which has length uniformly shorter than that shown in
FIG. 18B
by length x. On the other hand,
FIG. 18C
shows marks, each of which has length uniformly longer than that shown in
FIG. 18B
by length y. In either case shown in
FIGS. 18A and 18C
, no symmetry is observed in both marks and spaces. Because this asymmetry is also caused by fluctuations of laser wavelength, in general, it is difficult to adjust and maintain symmetry between pits and non-pits at the time of recording.
Now, the description is made on the specific hardware configuration and procedure
Konishi Shinichi
Minamino Jun-ichi
Miyashita Harumitsu
Nakajima Takeshi
Nakamura Atsushi
Greenblum & Bernstein P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Patel Gautam R.
LandOfFree
Waveform equalizer for a reproduction signal obtained by... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Waveform equalizer for a reproduction signal obtained by..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Waveform equalizer for a reproduction signal obtained by... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3245035