Error detection/correction and fault detection/recovery – Pulse or data error handling – Data formatting to improve error detection correction...
Reexamination Certificate
2000-05-25
2003-08-26
Ton, David (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Data formatting to improve error detection correction...
C369S047360
Reexamination Certificate
active
06611927
ABSTRACT:
BRIEF DESCRIPTION
The present invention relates generally to an optical Partial Response Maximum Likelihood (PRML) read channel, and particularly to an apparatus and method for error calculations and ideal value estimation in an optical PRML read channel.
BACKGROUND
DVD, an acronym for Digital Video Disc or Digital Versatile Disc, is a relatively new type of Compact-Disc Read-Only-Memory (CD-ROM) with a minimum capacity of approximately 4.7 gigabytes.
FIG. 1
illustrates in block diagram form apparatus for recording to and reading data from DVD
22
. Recording Unit
20
takes digital data represented by the m
k
signal and records it on DVD
22
. (The subscript “k” is used throughout to indicate generally a time-variant signal and the subscript “kn” indicates the value of a time-variant signal at a time k+n.) Recording Unit
20
includes an Eight-to-Fourteen Modulator (EFM)
21
. EFM
21
translates each block of 8 data bits represented by the m
k
signal into a block of 14 channel bits, selected for its specific bit pattern. To control the length of the pits on DVD
22
, EFM
21
uses only those 14 bit sequences that include two, but less than ten, consecutive
0
s. These constraints are referred to as (d=2, k=10) in DVD literature.
DVD player
24
includes Optical Pick-up Unit (OPU)
26
, Automatic Gain Control (AGC) & Equalization Circuitry
28
, Analog-to-Digital Converter (ADC)
34
, Viterbi Decoder
46
, and Clock
40
. OPU
26
converts information read from DVD
22
into an analog RF signal on line
27
. AGC & Equalization Circuitry
28
filters and limits the voltage magnitude of the EFM encoded RF signal on line
27
, producing the analog z
k
signal on line
33
. ADC
34
samples the EFM encoded analog signal on line
33
and produces a multi-bit digital, EFM encoded signal on line
35
. A single sample of an EFM encoded signal is referred to herein as an EFM datum. Viterbi Decoder
36
analyzes several EFM datums and determines the most likely value represented by each EFM datum. Clock
40
generates a clock signal, CK, from the digital signal on line
35
. The CK signal is used by AGC & Equalization Circuitry
28
, ADC
34
and Viterbi Decoder
46
.
Both Clock
40
and AGC & Equalization Circuitry
28
include Error Calculators
50
, which generate error signals used to improve circuit performance.
FIG. 2
illustrates prior art Error Calculator
50
in block diagram form. Error Calculator
50
receives the output signal from its associated circuit, the y
k
signal, from which an error signal, e
k
, is generated. A value of the y
k
signal at a time k is an EFM datum. Over several clock cycles the y
k
signal represents a sequence of EFM datums. Error Calculator
50
includes Quantizer
52
and Summer
54
. Quantizer
52
determines the ideal value, y
k
{circumflex over ( )}, for the EFM datum currently represented by the y
k
signal. Quantizer
52
determines the ideal value, y
k
{circumflex over ( )}, using Relationship (1).
y
k
{circumflex over ( )}=
q
*round(
y
k
/q
); (1)
where q represents a quantization interval; and “round” represents a rounding function.
Summer
54
determines the error of the input signal, y
k
, by subtracting it from the corresponding ideal value. Thus, the error signal, e
k
, is given by Expression (2).
e
k
=y
k
{circumflex over ( )}−
y
k
. (2)
Error signal estimation is adversely affected by baseline wandering of the z
k
signal (See FIG.
1
). As used herein, baseline wandering refers to low frequency disturbances of a radio frequency signal. Baseline wandering of the z
k
signal leads to errors in the y
k
signal, which in turn leads to errors in the ideal value signal, the y
k
{circumflex over ( )} signal. These errors degrade the performance of the AGC & Equalization Circuitry
28
and Clock
40
. Thus, a need exists for improved error signal calculation and ideal value estimation in Optical PRML read channels.
SUMMARY
The apparatus of the present invention improves ideal value estimation for Eight-Fourteen Modulated (EFM) data, thus enabling improved error calculations in an Optical PRML Reach Channel. The apparatus of the present invention includes a peak detector and modification circuitry. The peak detector receives a first set of signals representing initial values of a sequence of EFM datums, each of which has an initial value that is a member of a first set of values including {−b, −a, c, a, b} where |b|>|a|>|c|. The peak detector analyzes a first subsequence of the sequence of EFM datums to determine whether a peak has occurred and, if so, asserts a modify signal. The modification circuitry responds to assertion of the modify signal by replacing the initial values of a second subsequence of the sequence EFM datums with revised values. The second subsequence of EFM datums follows the first subsequence of EFM datums and each revised value of the second subsequence has an absolute value that is a member of the first set of values.
REFERENCES:
patent: 4423498 (1983-12-01), Kimura et al.
patent: 5072435 (1991-12-01), Bakx
patent: 5226027 (1993-07-01), Bakx
patent: 5303217 (1994-04-01), Bakx et al.
patent: 5623472 (1997-04-01), Bakx et al.
Oak Technology, Inc.
Pennie & Edmonds LLP
Ton David
LandOfFree
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