Electrical computers: arithmetic processing and calculating – Electrical digital calculating computer – Particular function performed
Reexamination Certificate
1999-01-06
2001-09-18
Mai, Tan V. (Department: 2121)
Electrical computers: arithmetic processing and calculating
Electrical digital calculating computer
Particular function performed
Reexamination Certificate
active
06292816
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an equalizing apparatus, and more particularly, to a non-linear equalizing apparatus used for a digital magnetic recording medium.
2. Description of the Related Art
Nonlinearity becomes a serious problem as recording density increases in a digital magnetic recording medium such as a hard disk drive (HDD). The nonlinearity is generated due to interaction between adjacent transitions. A demagnetization field of a previously recorded transition shifts the position of a subsequently recorded transition and increases the width between transitions. The adjacent transitions operate to erase each other. As a result, the size of a reproduced signal is reduced. Such phenomenons are known as nonlinear transition shift (NLTS), a transition broadening, and a partial erasure respectively.
When data are to be recorded, some peripheral bits generate such a nonlinear distortion. However, an interference effect between signals in reproduced signals exists in many bits. Accordingly, the nonlinear distortion affects many bits. When a signal detector does not process the nonlinear distortion, data detection reliability deteriorates.
According to a conventional technology (U.S. Pat. No. 5,132,988), the nonlinear distortion is processed using a feedback RAM instead of a feedback filter. Since a RAM model for processing the nonlinear distortion models only the nonlinear distortion from past data, it is impossible to consider the interaction between current and future data.
Also, since the size of a RAM is doubled as the range of data filtered by a feedback portion increases by one bit in this equalizer, the amount of data which can be processed by the feedback portion is restricted by the size of the RAM.
The linearity and nonlinearity characteristics of a channel are shown by three pulses in a paper by W. Zeng and J. Moon [“A Practical Nonlinear Model for Magnetic Recording Channels”, IEEE Trans. Magn., vol. 30, no. 6, pp. 4233-4235, November 1994]. The three pulses are an isolated transition response which is a transition response in the case that there is no transition between adjacent data and dibit responses which are transition responses in the case that there is a transition in a one bit past and there is a transition in a two bit past. The three pulses are obtained by measuring the reproduced signals.
However, a channel characteristic is not obtained from all the data sequences which may be generated but obtained by measuring a channel signal in an extremely restricted situation, in this model. As a result, this model does not provide a method of mathematically optimizing a model in order to heighten the reliability or obtaining the channel characteristic in a more general situation. Also, logic regulations for generating logic variables such as Q
k
, R
k
, ERA, and CHO required for operating the model are not mathematically induced but are created depending on the experience of the writers. The nonlinear equalizer in which the model provided by W. Zeng and J. Moon is used [“Decision feedback equalizer with pattern dependent dynamic threshold,” IEEE Trans. Magn., vol. 32, no. 4, pp. 3266-3273, July 1996] includes all the restrictions and problems which the model has.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an adaptive nonlinear equalizing apparatus.
It is another object of the present invention to provide a pattern dependent filter of the above apparatus.
It is still another object of the present invention to provide an adaptive nonlinear equalizing method which can effectively process a nonlinear distortion generated by an interaction not only between adjacent past bits but also between current and future bit data.
In order to achieve the first object, there is provided a nonlinear equalizing apparatus for detecting original data a
k
from an input value r
k
obtained by reproducing data received through a transfer channel or recorded on a storing apparatus, comprising a linear filter for linear filtering the input value r
k
, a pattern dependent filter including 2
&tgr;+v
tap values selected by the respective patterns (b
k−n+v:k−n+1
,b
k−n−1:k−n−&tgr;
) of future v and past &tgr; bit data transition absolute values and N taps p
n
(b
k−n+v:k−n+1
,b
k−n−1:k−n−&tgr;
) for outputting the value obtained by multiplying the selected tap value with the current transition (x
k−n
), and (wherein, x
k−n
=(a
k−n
−a
k−n−1
)/2∈{−1, 0, }, b
k−n
=|x
k−n
|∈{0, 1}, b
k−n−1:k−n−&tgr;
=(b
k−n−1
b
k−n−2
. . . b
k−n−&tgr;
), b
k−n+v:k−n+1
=(b
k−n+v
b
k−n+v−1
. . . b
k−n+1
), n=0, 1, 2, . . . , N, and N is a predetermined integer not less than 1+v) a detector for obtaining an error value e
k
by a subsequent equation, with respect to all combinations of current and future data sequences
e
k
=
∑
m
r
k
-
m
f
m
-
∑
n
x
k
-
n
p
n
(
b
k
-
n
+
v
:
k
-
n
+
1
,
b
k
-
n
-
1
:
k
-
n
-
τ
)
(wherein, ƒ
m
is the linear filter) and detecting current data assumed in the combination by which the minimum error square value is generated as the original data a
k
.
In order to achieve the second object, there is provided a pattern dependent filter, comprising the 0th through the Nth filter taps including 2
&tgr;+1
tap values selected by the pattern (b
k+1−n
,b
k−1−n:k−&tgr;−n
) of a future and past &tgr; bit data transition absolute values and adaptively renewed by the error value e
k−3
, for multiplying the selected tap value with the current transition x
k−n
and outputting the multiplication result, wherein a
k
is original data detected by the nonlinear equalizing apparatus, x
k−n
=(a
k−n
−a
k−n−1
)/2∈{−1, 0, }, b
k−n
=|x
k−n
|∈{0, 1}, b
k−n−1:k−n−&tgr;
=(b
k−n−1
b
k−n−2
. . . b
k−n−&tgr;
), n=0, 1, 2, . . . , N, and N is a predetermined integer not less than 2, wherein the respective filter taps comprises a buffer list for storing 2
&tgr;+1
tap values, tap value selecting means for selecting one among 2
&tgr;+1
tap values output from the buffer list by the pattern (b
k+1−n
,b
k−1−n:k−&tgr;−n
) of future one and past &tgr; bit data transition absolute values, a current transition multiplier for multiplying the tap value selected by the tap value selecting means with the current transition x
k−n
and outputting the result, and a tap value renewing means for renewing the tap value by adding the tap value selected by the pattern (b
k−2−n
,b
k−4−n:k−3−&tgr;−n
) of the past one and future &tgr; bit data transition absolute values from a reference time when the reference time is k−3−n.
In order to achieve the third object, there is provided a method of detecting original data a
k
from an input value r
k
obtained by reproducing data received through a transfer channel or recorded on a storing apparatus, comprising the steps of obtaining
∑
n
r
k
-
n
f
n
by linear filtering the input value r
k
, obtaining
z
k
=
∑
n
r
k
-
n
f
n
-
∑
n
=
2
N
x
k
-
n
p
n
(
b
k
-
n
+
1
,
b
k
-
n
-
1
:
k
-
n
-
τ
)
from already known data when a filter tap including 2
&tgr;+1
tap values selected by the pattern (b
k+1−n
,b
k−1−n:k−&tgr;−n
) of the future one and past &tgr; bit data transition absolute values from a reference time when the reference time is k−n for multiplying
Burns Doane Swecker & Mathis L.L.P.
Mai Tan V.
Samsung Electronics Co,. Ltd.
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