ICS1892 Datasheet, PDF (47/148 Pages) Integrated Circuit Systems – 10Base-T/100Base-TX Integrated PHYceiver

ICS1892
Chapter 7 Functional Blocks
7.4.4 100Base-TX Operation: Adaptive Equalizer
The ICS1892 TP-PMD sublayer employs adaptive equalization circuitry to compensate for signal amplitude
and phase distortion incurred from the transmission medium. At a data rate of 100 Mbps, the transmission
medium (that is, the cable) introduces significant signal distortion because of high-frequency attenuation
and phase shift. The high-frequency loss occurs primarily because of the cable skin effect that causes the
conductor resistance to rise as the square of the frequency rises.
In shielded twisted-pair (STP) and unshielded twisted-pair (UTP) category 5 cables with maximum lengths
of 130 meters, the ICS1892 adaptive equalizer accurately compensates for these losses.
For a UTP Category 5 cable that is 100 meters long (the maximum length as per the EIA/TIA-568-A
standard), there are three distinct levels to resolve to recover the MLT-3 encoded data. As a result, the
pulse shape of the received signal is critical.
The ICS1892 employs a DSP-based adaptive equalization technique to compensate for a wide range of
cable lengths. The optimizing parameter for the equalizer adaptation process is the overall ICS1892 bit
error rate, which provides the ICS1892 with a very high overall reliability.
7.4.5 100Base-TX Operation: Twisted-Pair Transmitter
For both 10Base-T and 100Base-TX operations, the ICS1892 uses the same Twisted-Pair Transmit pins
(TP_TXP and TP_TXN) as well as the same internal functional module. The twisted-pair transmitter
module is a current-driven, differential driver that can supply either of the following:
• A two-level 10Base-T (that is, Manchester-encoded) signal
• A three-level 100Base-TX (that is, MLT-3 encoded) signal
The ICS1892 interfaces with the medium through an isolation transformer (also called a magnetic module).
The ICS1892 transmitter uses wave-shaping techniques to control the output signal rise and fall times
(thereby eliminating the need for expensive external filters) and interfaces directly to the isolation
transformer.
Note:
1. In reference to the ICS1892, the term ‘Twisted-Pair Transmitter’ refers to the set of Twisted-Pair
Transmit output pins (TP_TXP and TP_TXN).
2. For information on the 10Base-T Twisted-Pair Transmitter, see Section 7.5.11, “10Base-T Operation:
Twisted-Pair Transmitter”.
7.4.6 100Base-TX Operation: Twisted-Pair Receiver
Twisted-Pair Receiver operations are similar to Twister-Pair Transmitter operations, in that for both
10Base-T and 100Base-TX operations, the ICS1892 uses the same Twister-Pair Receive pins (TP_RXP
and TP_RXN).
However, unlike the transmitter operations (which use the same internal functional module), the ICS1892
employs separate internal twisted-pair receiver modules to process the incoming data: one for 10Base-T
operations and one for 100Base-TX operations. The internal twisted-pair receiver modules interface with
the medium through an isolation transformer. The 100Base-TX receiver module accepts and processes a
differential three-level 100Base-TX (that is, MLT-3 encoded) signal from the isolation transformer.
Note:
1. In reference to the ICS1892, the term ‘Twisted-Pair Receiver’ refers to the set of Twisted-Pair Receive
output pins (TP_RXP and TP_RXN).
2. For information on the 10Base-T Twisted-Pair Receiver, see Section 7.5.12, “10Base-T Operation:
Twisted-Pair Receiver”.
ICS1892, Rev. D, 2/26/01
© 2000-2001, Integrated Circuit Systems, Inc.
All rights reserved.
47
February 26, 2001