U.S. patent application number 11/691518 was filed with the patent office on 2007-12-13 for read channel apparatus and method for an optical storage system.
This patent application is currently assigned to MEDIATEK INC.. Invention is credited to Ke-Chiang Huang, Tzu-Pai Wang.
Application Number | 20070286270 11/691518 |
Document ID | / |
Family ID | 25485650 |
Filed Date | 2007-12-13 |
United States Patent
Application |
20070286270 |
Kind Code |
A1 |
Huang; Ke-Chiang ; et
al. |
December 13, 2007 |
READ CHANNEL APPARATUS AND METHOD FOR AN OPTICAL STORAGE SYSTEM
Abstract
A read channel apparatus is disclosed for reading data recorded
on an optical storage system at a predetermined baud rate. The
apparatus asynchronously samples an analog read signal generating
from the optical storage system and subtracts an estimated DC
offset from the asynchronous sample values to generate a sequence
of asynchronous DC-removed sample values. The asynchronous
DC-removed sample values are separately interpolated by two
interpolators to generate a sequence of synchronous even-time
sample values and a sequence of synchronous odd-time sample values
respectively. The synchronous even-time and odd-time sample values
are separately equalized by two equalizers in accordance with a
target spectrum to generate a sequence of even-time equalized
sample values and a sequence of odd-time equalized sample values
respectively. A DC offset estimator generates the estimated DC
offset from the even-time equalized sample values and the odd-time
equalized sample values. The interpolators are under the control of
a timing recovery controller for synchronizing the even-time and
odd-time sample values to the baud rate. In the preferred
embodiment, the recorded data are determined from the even-time
equalized sample values and the odd-time equalized sample
values.
Inventors: |
Huang; Ke-Chiang; (Taipei
Hsien, TW) ; Wang; Tzu-Pai; (Taipei Hsien,
TW) |
Correspondence
Address: |
THOMAS, KAYDEN, HORSTEMEYER & RISLEY, LLP
600 GALLERIA PARKWAY
STE 1500
ATLANTA
GA
30339
US
|
Assignee: |
MEDIATEK INC.
No. 1, Dusing Rd. 1st Science-Based Industrial Park
Hsin-Chu
TW
300
|
Family ID: |
25485650 |
Appl. No.: |
11/691518 |
Filed: |
March 27, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11126991 |
May 11, 2005 |
7212567 |
|
|
11691518 |
Mar 27, 2007 |
|
|
|
09947169 |
Sep 5, 2001 |
6904084 |
|
|
11126991 |
May 11, 2005 |
|
|
|
Current U.S.
Class: |
375/229 ;
G9B/20.01; G9B/20.012 |
Current CPC
Class: |
G11B 20/1403 20130101;
G11B 20/10009 20130101; G11B 20/10037 20130101; G11B 20/10046
20130101; H04L 7/0029 20130101; G11B 20/10203 20130101 |
Class at
Publication: |
375/229 |
International
Class: |
H03K 5/00 20060101
H03K005/00 |
Claims
1. A read channel apparatus for reading data at a predetermined
baud rate, comprising: a sampling device for asynchronously
sampling an analog read signal to generate a sequence of
asynchronous sample values; a first interpolator for interpolating
the asynchronous sample values to generate a sequence of
synchronous even-time sample values substantially synchronized to
one-half the baud rate; a second interpolator for interpolating the
asynchronous sample values to generate a sequence of synchronous
odd-time sample values substantially synchronized to one-half the
baud rate; and a timing recovery controller, responsive to the
even-time sample values and the odd-time sample values, for
controlling the first interpolator and the second interpolator
respectively in order to synchronize the even-time and odd-time
sample values to the baud rate; wherein the recorded data are
determined from the even-time sample values and the odd-time sample
values.
2. The read channel apparatus of claim 1, further comprising a
sequence detector for detecting the recorded data from the
even-time sample values and the odd-time sample values.
3. The read channel apparatus of claim 2, wherein the sequence
detector comprises a Viterbi sequence detector.
4. The read channel apparatus of claim 1, wherein the sampling
device samples the analog read signal at a sampling rate slightly
above 1/2 the baud rate of the recorded data.
5. The read channel apparatus of claim 4, wherein the sampling
device comprises an analog-to-digital converter.
6. The read channel apparatus of claim 1, further comprising: a DC
offset estimator for generating an estimated DC offset from the
even-time sample values and the odd-time sample values; and a
subtractor for subtracting the estimated DC offset from the
asynchronous sample values.
7. The read channel apparatus of claim 1, further comprising: a
first equalizer for equalizing the synchronous even-time sample
values in accordance with a target spectrum; and a second equalizer
for equalizing the synchronous odd-time sample values in accordance
with the target spectrum.
8. The read channel apparatus of claim 7, wherein coefficients of
the first equalizer and coefficients of the second equalizer are
the same.
9. The read channel apparatus of claim 8, wherein the first and
second equalizers are 2T-spaced equalizers where T stands for a
baud rate interval of the recorded data.
10. A read channel method for reading data at a predetermined baud
rate, comprising: asynchronously sampling an analog read signal to
generate a sequence of asynchronous sample values; separately
interpolating the asynchronous sample values to respectively
generate a sequence of synchronous even-time sample values
substantially synchronized to one-half the baud rate and a sequence
of synchronous odd-time sample values substantially synchronized to
one-half the baud rate; and detecting the recorded data from the
even-time sample values and the odd-time sample values.
11. The read channel method of claim 10, wherein the detecting step
performs a run length limitation with Viterbi detection to
determine the recorded data from the even-time sample values and
the odd-time sample values.
12. The read channel method of claim 10, wherein the sampling step
samples the analog read signal at a sampling rate slightly above
1/2 the baud rate of the recorded data.
13. The read channel method of claim 10, further comprising:
generating an estimated DC offset from the even-time sample values
and the odd-time sample values; and subtracting an estimated DC
offset from the asynchronous sample values.
14. The read channel method of claim 10, further comprising:
separately equalizing the synchronous even-time and odd-time sample
values in accordance with a target spectrum to respectively.
15. A read channel apparatus for reading data recorded at a
predetermined baud rate, comprising: a sampling device for
asynchronously sampling an analog read signal to generate a
sequence of asynchronous sample values; N interpolators for
interpolating the asynchronous sample values to generate N sets of
synchronous sample values, wherein the N sets of synchronous sample
values form a sequence of synchronous sample values substantially
synchronized to the baud rate; and a timing recovery controller,
responsive to the N sets of synchronous sample values, for
controlling the N interpolators respectively in order to
synchronize the N sets of synchronous sample values to the baud
rate; wherein the recorded data are determined from the N sets of
synchronous sample values.
16. The read channel apparatus of claim 15, further comprising a
sequence detector for detecting the recorded data from the N sets
of synchronous sample values.
17. The read channel apparatus of claim 15, further comprising an
equalizer equalizing the N sets of synchronous sample values in
accordance with a target spectrum to generate N sets of equalized
sample values.
18. The read channel apparatus of claim 17 further comprising a
sequence detector for detecting the recorded data from the N sets
of equalized sample values.
19. The read channel apparatus of claim 18, wherein the sequence
detector comprises a Viterbi sequence detector.
20. The read channel apparatus of claim 15, wherein the sampling
device samples the analog read signal at a sampling rate slightly
above 1/2 the baud rate of the recorded data.
21. The read channel apparatus of claim 20, wherein the sampling
device comprises an analog-to-digital converter.
22. The read channel apparatus of claim 15, further comprising: a
DC offset estimator for generating an estimated DC offset from the
N sets of synchronous sample values; and a subtractor for
subtracting the estimated DC offset from the asynchronous sample
values.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/126,991 filed on May 11, 2005, which is a
continuation of U.S. patent application Ser. No. 09/947,169, filed
Sep. 5, 2001, which is issued as U.S. Pat. No. 6,904,084.
FIELD OF THE INVENTION
[0002] The present invention relates generally to an optical
storage system and, in particular, to a read channel apparatus and
method for an optical storage system.
BACKGROUND OF THE INVENTION
[0003] In recent years, the development of new optical recording
media and data compression techniques has made it possible to
achieve enormous data storage capacity using optical storage
systems. Optical storage systems are used to store audio
information, such as in Compact Disk (CD) players, as well as
visual and computer information, such as in CD-ROM and the more
recent Digital Video Disk (DVD) players. The information is
typically recorded as a binary sequence by writing a series of
"pits" on the optical medium which represent binary "1" and "0"
bits. When reading this recorded data, a pick-up head (transducer),
positioned in close proximity to the rotating disk, detects the
alternations on the medium and generates an analog read signal. The
analog read signal is then detected and decoded by read channel
circuitry to reproduce the recorded data.
[0004] To improve performance of the read channel in an optical
storage system, the sampled amplitude techniques are applied.
Sampled amplitude read channels commonly employ an
analog-to-digital converter (ADC) and a digital read channel
processor to reproduce data recorded on the optical storage
systems. However, in high-speed optical storage systems, the baud
rate (channel bit rate) is very high such that sampling frequency
of ADC and clock of digital processor also need comparable high
clock rate sources. This is not desirable since operating the
channel at higher frequencies increases its complexity and cost.
There is, therefore, a need for a sampled amplitude read channel
for use in storage systems that can operate at high data rates and
densities without increasing the cost and complexity of the read
channel ICs. To this end, U.S. Pat. No. 5,802,118 (Bliss et al.)
discloses a sub-sampled discrete time read channel for magnetic
disk storage systems. According to this patent, the read channel
sub-samples an analog signal at a rate less than or equal to 9/10
the baud rate. K. C. Huang, the inventor of present invention,
discloses a sub-sampled method for read channel of an optical
storage system in Taiwan patent application No. 089,110,848, filed
in June 2000. The prior art sub-samples an analog signal at a rate
slightly above 1/2 the baud rate. The sub-sampled values are
down-sampled by a timing recovery interpolator to generate sample
values synchronized to one-half the baud rate. The synchronous
sample values are then equalized by a 2T-spaced equalizer and
interpolated by a factor-two upsampler. Although it significantly
reduces the sampling frequency, the latency time introduced by the
upsampler causes significant degradation in the performance of the
high-speed optical storage systems.
[0005] For the reasons mentioned above, a novel read channel
apparatus and method is provided to reproduce data recorded on the
optical storage systems, unencumbered by the limitations associated
with the prior art.
SUMMARY OF THE INVENTION
[0006] It is one object of the present invention to provide a read
channel apparatus and method for an optical storage system which
sub-samples an analog read signal at a rate slightly above one-half
the baud rate to reduce clock rate of the read channel.
[0007] It is another object of the present invention to provide a
read channel apparatus and method for an optical storage system
that reproduces recorded data with better performance by getting
rid of the latency of up-sampling.
[0008] To achieve the above object of the present invention, there
is provided a read channel apparatus and method for reading data
recorded on an optical storage system at a predetermined baud rate.
The read channel apparatus includes a sampling device, a
subtractor, two interpolators, two equalizers, and a DC offset
estimator. The sampling device asynchronously samples an analog
read signal generating from the optical storage system to generate
a sequence of asynchronous sample values. The subtractor subtracts
an estimated DC offset from the asynchronous sample values to
generate a sequence of asynchronous DC-removed sample values. Then,
the first interpolator interpolates the asynchronous DC-removed
sample values to generate a sequence of synchronous even-time
sample values substantially synchronized to one-half the baud rate.
The second interpolator also interpolates the asynchronous
DC-removed sample values to generate a sequence of synchronous
odd-time sample values substantially synchronized to one-half the
baud rate. Thereafter, the first equalizer equalizes the
synchronous even-time sample values in accordance with a target
spectrum to generate a sequence of even-time equalized sample
values. The second equalizer equalizes the synchronous odd-time
sample values in accordance with the target spectrum to generate a
sequence of odd-time equalized sample values. Besides, a DC offset
estimator generates the estimated DC offset from the even-time
equalized sample values and the odd-time equalized sample values.
The two interpolators are under the control of a timing recovery
controller for synchronizing the even-time and odd-time sample
values to the baud rate. In a preferred embodiment, a sequence
detector detects the recorded data from the even-time equalized
sample values and the odd-time equalized sample values.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The above and other aspects and advantages of the present
invention will be better understood by reading the following
detailed description of the invention in conjunction with the
drawings, wherein:
[0010] FIG. 1 is a block diagram illustrating a read channel in
accordance with the present invention;
[0011] FIG. 2A shows the asynchronous sample values A.sub.K sampled
from an analog read signal A(t);
[0012] FIG. 2B shows the synchronous even-time sample values
X.sub.2K substantially synchronized to 1/2 the baud rate;
[0013] FIG. 2C shows the synchronous odd-time sample values
X.sub.2K+1 substantially synchronized to 1/2 the baud rate;
[0014] FIG. 2D shows the even-time equalized sample values
Y.sub.2K;
[0015] FIG. 2E shows the odd-time equalized sample values
Y.sub.2K+1;
[0016] FIG. 2F shows a sequence Y.sub.K composed of Y.sub.2K and
Y.sub.2K+1 wherein all sample values are substantially synchronized
to the baud rate; and
[0017] FIG. 2G shows a binary sequence Z.sub.K determined by a
sequence detector.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] With reference to FIGS. 1 and 2A.about.2G, the present
invention will become more apparent from the following detailed
description. A read channel apparatus 200 for reading data recorded
on an optical storage system at a predetermined baud rate is shown
in FIG. 1. The analog read signal A(t), generating from the optical
storage system, is asynchronously sampled by a sampling device 202
(e.g., an analog-to-digital converter) to generate a sequence of
asynchronous sample values A.sub.K. The sampling device 202 is
clocked at a constant frequency fs by a sampling clock 240
generated by a clock source 220. The sequence of asynchronous
sample values A.sub.K is related to the analog read signal A(t) as
A.sub.K={ . . . , A(0), A(.sub.T), A(2.sub.T), . . . , A(k.sub.T),
. . . } where k is an integer and .sub.T=1/fs. In FIG. 2A, the
analog read signal is shown as a solid line, and the asynchronous
sample values A.sub.K are shown as black dots. It should be noted
that T, as depicted in FIGS. 2A.about.2G, denotes the baud rate
interval and 1/T denotes the baud rate. Since the frequency
spectrum of the analog read channel A(t) received from the read
transducer is bandlimited to about 1/4T. Thus, the sampling device
202 only needs to sample the analog read signal A(t) at a rate
slight above 1/2 the baud rate, i.e., fs>1/2T, rather than
synchronous sampling at the baud rate. In FIG. 2A, for instance,
the analog read signal A(t) is sampled at 4/7 the baud rate.
[0019] With continued reference to FIG. 1, a subtractor 204
subtracts an estimated DC offset, over line 230, from the
asynchronous sample values A.sub.K to generate a sequence of
asynchronous DC-removed sample values B.sub.K. This can be denoted
as B.sub.K={ . . . , B(0), B(.sub.T), B(2.sub.T), . . . ,
B(k.sub.T), . . . } and B(k.sub.T)=A(k.sub.T)-DC where DC denotes
the estimated DC offset.
[0020] According to the present invention, the first interpolator
206a interpolates the asynchronous DC-removed sample values B.sub.K
and generates a sequence of synchronous even-time sample values
X.sub.2K substantially synchronized to one-half the baud rate. The
second interpolator 206b also interpolates the asynchronous
DC-removed sample values B.sub.K to generate a sequence of
synchronous odd-time sample values X.sub.2K+1 substantially
synchronized to one-half the baud rate. As depicted in FIGS. 2B and
2C, the synchronous even-time sample value X.sub.2K is shown as
".DELTA." and the synchronous odd-time sample value X.sub.2K+1 is
shown as "x". The synchronous even-time and odd-time sequences can
be denoted as X.sub.2K={ . . . , X(0), X(2T), X(4T), . . . ,
X(2kT), . . . } and X.sub.2k+1={ . . . , [[X(1)]]X(T), X(3T),
X(5T), . . . , X((2k+1)T), . . . } where k is an integer and T is
the baud rate interval. Hence, the synchronous even-time sequence
X.sub.2K has a spacing between samples equal to 2T and the
synchronous odd-time sequence X.sub.2K+1 also has a spacing between
samples equal to 2T. For more details concerning the interpolators
206a and 206b, refer to F. M. Gardner, "Interpolation in Digital
Modems--Part I: Fundamentals", IEEE Trans. Commun., Vol. 41, pp.
502-508, March 1993; and L. Erup, F. M. Gardner, and R. A. Herris,
"Interpolation in Digital Modems--Part II: Implementation and
performance", IEEE Trans. Commun., Vol. 41, pp. 998-1008, June
1993.
[0021] The synchronous even-time and odd-time sequences are
separately equalized according to a target spectrum. That is, the
high-frequency components of X.sub.2K and X.sub.2K+1 are enhanced
by equalization. This can be implemented with, for instance, two
5-tap symmetric 2-T spaced equalizers. A first 2T-spaced equalizer
208a equalizes the synchronous even-time sample values X.sub.2K in
accordance with the target spectrum to generate a sequence of
even-time equalized sample values Y.sub.2K. The second 2T-spaced
equalizer 208b equalizes the synchronous odd-time sample values
X.sub.2K+1 in accordance with the target spectrum to generate a
sequence of odd-time equalized sample values Y.sub.2K+1. The first
and second 2T-spaced equalizers preferably employ the same
coefficients. Referring to FIGS. 2D and 2E, the even-time and
odd-time equalized sequences can be represented by Y.sub.2K={ . . .
, Y(0), Y(2T), Y(4T), . . . , Y(2kT), . . . } and Y.sub.2K+1={ . .
. , [[Y(1)]]Y(T), Y(3T), Y(5T), . . . , Y((2k+1)T), . . . }
[0022] The even-time and odd-time equalized sequences are fed back
to a timing recovery controller 210 and a DC offset estimator 212.
The timing recovery controller 210 respectively controls the first
interpolator 206a and the second interpolator 206b, in response to
Y.sub.2K and Y.sub.2K+1 received over line 226 and line 228, to
synchronize the even-time and odd-time sample values to the baud
rate. The DC offset estimator 212, in response to Y.sub.2K and
Y.sub.2K+1 received over line 232 and line 234, generates the
estimated DC offset.
[0023] Referring to FIGS. 2F and 2G, if the quality (e.g.,
signal-to-noise ratio) of the analog read signal is good enough, an
estimated binary sequence Z.sub.K representing recorded data can be
determined directly from Y.sub.K. The sequence Y.sub.K is composed
of Y.sub.2K and Y.sub.2K+1 as illustrated in FIG. 2F. For example,
the m-th bit of Z.sub.K is estimated to be "1" if Y(mT)>0, and
"0" if y(mT)<0. However, if the quality of the analog read
signal is poor, a sequence detector 214 is preferably applied to
detect the sequence Z.sub.K from Y.sub.2K and Y.sub.2K+1. The
sequence detector 214 typically utilizes the Viterbi algorithm to
implement the run length limitation of DVD systems. In DVD, the
minimum run length is 3, that is, the sequence with " . . . 0001000
. . . ", " . . . 00011000 . . . ", " . . . 1110111 . . . " and " .
. . 11100111 . . . " are not allowed in DVD and will be filtered
out by the sequence detector 214. Thus, the read channel apparatus
200 as described above, processes the even-time and odd-time sample
values separately so that it avoids degrading in performance caused
by an up-sampling latency.
[0024] The objects of the invention have been fully realized
through the preferred embodiment disclosed herein. It will be
apparent that the invention is not limited thereto, and that many
modifications and additions may be made within the scope of the
invention. Therefore, it is the object of the appended claims to
cover all such variations and modifications as come within the true
spirit and scope of the invention.
* * * * *