Digital Signal Processing Reference
In-Depth Information
50
30
10
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10
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30
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−
70
−
−
90
6800
7300
7800
Time (ps)
8300
Figure 12-31
Differential pulse response with equalization for Example 12-5.
150
120
90
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30
0
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30
−
60
−
90
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120
−
150
0
5
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15
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Time (ps)
Figure 12-32
Equalized differential data eye for Example 12-5.
The chief limitation of the zero forcing approach is that for a finite-length
equalizer, minimization of the ISI is guaranteed only if the eye is initially open, a
condition that is not necessarily true for long, lossy channels such as backplanes.
An approach that avoids the limitation of the ZFS algorithm is the minimum
mean-square error (MMSE) algorithm. This approach sets the equalizer coeffi-
cients such that the mean-square error of the ISI is minimized at the output of
the equalizer. Examination of the MMSE equalizer is left for Problem 12-7, and
a thorough treatment of both the ZFS and MMSE methods is given by Proakis
[2001].
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