14
ICS1890
0.1
1
10
100
30
20
10
0
typical
worst case
Cable Attenuation (dB) v. Freq. (MHz)
Figure 3
Figure 4
Typical and worst case frequency response for 100 meters
(worst case length as derived from draft standard EIA/TIA-
568- A) of UTP Category 5 cable is shown in Figure 3.
The pulse shape of the received signal is critical for MLT-3
encoded data since there are three distinct levels to resolve in
order to properly recover the data. Figure 4 shows the typical
signal at the input and output ends of 100 meters of UTP
Category 5 cable.
Since the cable length that must be equalized can be anything
from 0 to 105 meters, the optimum equalization cannot be fixed,
but must depend on cable length. Thus, adaptive equalization
must be applied at the receive end to restore the signal.
The adaptive equalization process consists of applying increasing
amounts of phase and gain correction while monitoring the
integrity of the recovered data. The adaptive equalizer picks
the best of 32 equalization settings and Fixes this value into
the equalization register. This setting provides the best recovery
of the transmitted data with lowest Bit Error Rate (BER).
Line Transmitter
The line transmitter logic of the
ICS1890
is a current-driven differential driver which can be programmed
for either two-level (10Base-T, Manchester) or three-level
(100Base-TX, MLT-3) transmission. Waveshaping is applied
to control the output edge rate and eliminate the need for
expensive external filters. The transmitter interfaces directly to
an inexpensive isolation transformer (magnetics).
Line Receiver
The line receiver circuit accepts either a
differential two-level (10Base-T, Manchester) or three-level
(100Base-TX, MLT-3) signal which first passes through an
isolation transformer. If the polarity correct bit in the Configuration
Register is asserted, the
ICS1890
has sensed the reversed
polarity of the receive pair and can switch polarity automatically.
Magnetics
A Universal Magnetics module is used to provide
isolation and signal coupling onto the twisted pair cabling for
both 10Base-T and 100Base-TX.
Summary of Contents for PHYceiver ICS1890
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