Datasheet

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DP83865
4.0 Functional Description (Continued)
4.3.4 Baseline Wander (BLW) Correction
Baseline wander is the slow variation of the DC level of the
incoming signal due to the non-ideal electrical characteris-
tics of the magnetics and the inherent DC component of
the transmitted waveform. The BLW correction circuit uti-
lizes the slicer error signal to estimate and correct for BLW.
4.3.5 Slicer
The Slicer selects the PAM-5 symbol value (+2,+1,0,-1,-2)
closest to the voltage input value after the signal has been
corrected for line Inter Symbol Interference (ISI), attenua-
tion, echo, crosstalk and BLW.
The slicer produces an error output and symbol value deci-
sion output. The error output is the difference between the
actual voltage input and the ideal voltage level represent-
ing the symbol value. The error output is fed back to the
BLW, AGC, Crosstalk Canceller and Echo Canceller sub
blocks to be used in their respective algorithms.
4.4 1000BASE-T PCS Receiver
The PCS Receiver consists of several sub functional
blocks that convert the incoming quartet of quinary sym-
bols (PAM-5) data from the PMA Receiver A, B, C, and D to
8-bit receive data (RXD[7:0]), data valid (RX_DV), and
receive error (RX_ER) signals on the GMII. The block dia-
gram of the 1000BASE-T Functional Block in section
“ Block Diagram” on page 2 provides an overview of the
Figure 3. PMA Transmitter Block
Figure 4. Effect on Spectrum of PR-shaped PAM-5 coding
0.75 0.25
Z
-1
TABLE
LOOKUP
17-LEVEL
PAM-5
5-bits/sample
DAC
CONTROL
20-bits/sample
1000
MLT-3/PAM-17
ANALOG
PARTIAL RESPONSE PULSE SHAPE CODING
5-LEVEL PAM-5 TO 17-LEVEL PAM
0.75∗X(k) + 0.25∗X(k-1)
SIGN
SCRAMBLER
PAM-5
3-bits/sample
DAC
2-bit MLT-3
PMA Transmitter Block
Manchester/
Manchester coding
MUX
100
10
Transmit Spectra
-0.400
-0.200
0.000
0.200
0.400
0.600
0.800
1.000
1.200
10.00 100.00
Frequency (MHz)
Relative Amplitude
PAM-5 with PR (.75+.25T) PAM-5
critical region -- (30MHz -- 60MHz)