Coded data generation or conversion – Digital code to digital code converters – With error detection or correction
Reexamination Certificate
2003-05-12
2004-05-18
Tokar, Michael (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
With error detection or correction
C341S058000, C341S059000, C714S786000, C714S792000, C375S213000, C375S213000, C360S048000, C360S053000
Reexamination Certificate
active
06737998
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and a device for correcting a signal, and more particularly to a method and a device for correcting an analog signal outputted from a partial response channel to target levels.
BACKGROUND OF THE INVENTION
Optical disks such as compact disks (CDs), video compact disks (VCDs) and digital versatile disk (DVDs) are played by recording and reproducing devices such as VCD or DVD players. In a typical digital data recording and reproducing system of
FIG. 1
, a digital data sequence u is encoded by an error control encoder
11
and then modulated by a modulator
12
so as to be modified as a recording signal x. The recording signal x is suitable to be written into a digital data recording medium
10
by means of a write-in device
13
, and read out by a pickup head
14
. The signal read by the pickup head
14
is processed by an equalizer
15
into a signal y, and then the equalized signal y is processed by a detector
16
according to a sequential maximum likelihood algorithm into a read-out signal x′ in the same format as that of the recording signal x. The maximum likelihood algorithm, which is usually implemented as a Viterbi decoder, is well known in the art and need not be further described in detail herein. The read-out signal x′ is subsequently demodulated and decoded by a demodulator
17
and an error control decoder
18
, respectively, so as to obtain a recovered data sequence u′. Generally, the equalizer
15
, the detector
16
, the demodulator
17
and the error control decoder
18
are incorporated in a control chip of an optical disk drive.
The procedures for converting the recording signal x into the signal y will be illustrated in reference to
FIGS. 2 and 3
. In
FIG. 2
, the means for processing the recording signal x prior to entering the equalizer
15
can be simplified as a channel
20
The transfer function between the input/output signals x and z of the channel
20
is referred to as Z(D)/X(D)=1+a
1
*D+a
2
*D
2
+a
3
*D
3
+a
4
*D
4
+ . . . +a
n−1
*D
n−1
in a form of polynomial, where D is a delay time. The equalizer
15
is employed to remove some items of higher power in the polynomial, and thus the channel
20
and the equalizer
15
are viewed as an integrated partial response channel. For this partial response channel, a transfer function, for example PR(
1
,
1
), PR(
1
,
2
,
1
) or PR(
1
,
1
,
1
,
1
), can be applied for the transfer from the signal x to the signal y. The transfer function PR(
1
,
1
) indicates Y(D)/X(D)=1+D with target levels of −1, 0 and 1. The transfer function PR(
1
,
2
,
1
) indicates Y(D)/X(D)=1+2*D+D
2
with target levels of −2, −1, 1 and 2. The transfer function PR(
1
,
1
,
1
,
1
) indicates Y(D)/X(D)=1+D+D
2
+D
3
with target levels of −2, −1, 0, 1, 2.
The function PR(
1
,
1
) is unsatisfactory for being applied to real products because the noise cannot be effectively filtered out. Although the function PR(
1
,
1
,
1
,
1
) can result in good performance of the partial response channel, the cost thereof is relatively high. Thus, the function PR(
1
,
2
,
1
) is discussed hereinafter.
FIGS.
3
(
a
) to
3
(
c
) are timing waveform diagrams illustrating the corresponding signals processed in the partial response channel based on the transfer function PR(
1
,
2
,
1
). As shown in FIG.
3
(
a
), the recording signal x consists essentially of levels 0.5 and +0.5. The ideal waveform of the signal y, i.e. y
id
, after being processed by the partial response channel on the basis of the transfer function PR(
1
,
2
,
1
), i.e. Y(D)/X(D)=1+2*D+D
2
, is shown in FIG.
3
(
b
). The signal is supposed to be distributed at target levels of −2, 1, 1 and 2. However, the waveform of the signal y is practically somewhat drifted from the ideal target levels due to the mismatch between ideal partial response channel and real one. The real waveform of the signal y. i.e. y
real
, can for example be seen in FIG.
3
(
c
).
As shown, in spite of precise location on the four target levels −2, −1, 1, 2 for most of the sampled points, some sampled points are drifted from the target levels. Particularly for three sequential sampled points respectively in response to three sampling cycles, which are so-called as
3
T sampled points and for example include sampled points a, b and c as shown in FIG.
3
(
c
), the middle sampled point b is possibly greatly deviated from its target level −2 due to the significant variation during a short period of time. Under this circumstance, a mismatch problem occurs. When the mismatched signal y from the partial response channel is sent to the detector
16
, the read-out signal x′ may not be recovered to its original state as the recording signal x by a maximum likelihood algorithm.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and a device for correcting an analog signal from a partial response channel, which effectively locate three sequential and then correct the middle sampled point to a target level.
In accordance with an aspect of the present invention, there is provided a method for correcting an analog signal to target levels. The analog signal is transmitted from a partial response channel and comprises a plurality of periodically sampled points. The method for correcting an analog signal to target levels comprising steps of picking up three sequentially sampled points according to a specified criterion, and adjusting a middle one of the three sequentially sampled points to one of the target levels.
In an embodiment, the analog signal is a radio frequency (RF) signal.
In an embodiment, the analog signal is obtained by Y(D)=X(D)*(1 +2*D+D
2
), where D is a delay time, and X(D) is an input of the partial response channel. The analog signal is to be corrected into four target levels −2, −1, 1 and 2.
In an embodiment, the three sequentially sampled points have respective levels less than a threshold value, immediately follow one sampled point having a level greater than the threshold value, and are followed by one sampled point having a level greater than the threshold value. The middle one of the three sequentially sampled points is adjusted to a smallest one of the target levels. Preferably, the threshold value is “0”, and the smallest target level is “−2”.
Alternatively, the three sequentially sampled points have respective levels greater than a threshold value, immediately follow one sampled point having a level less than the threshold value, and are followed by one sampled point having a level less than the threshold value. The middle one of the three sequentially sampled points is adjusted to a largest one of the target levels. Preferably, the threshold value is “0”, and the largest target level is “2”.
In accordance with another aspect of the present invention, there is provided a method for correcting an analog signal to target levels. Firstly, the analog signal is periodically sampled to obtain a plurality of sampled points. Then, levels of the sampled points are compared with a threshold value to find a set of sequentially sampled points including a head and a tail ones, each having a first comparing result with the threshold value, and the other intermediate ones, each having a second comparing result with the threshold value. Then, one of the set of sequentially sampled points, which has the second comparing result with the threshold value, is adjusted to one of the target levels.
In an embodiment, the set of sequentially sampled points includes five consecutive sampled points.
In an embodiment, the first comparing result indicates that the level of each of the head and tail sampled points is greater than the threshold value, and the second comparing result indicates that the level of each of the intermediate sampled points is less than the threshold value. The step of adjusting
Madson & Metcalf
Mai Lam
Tokar Michael
Via Technologies Inc.
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