ICS1893CF datasheet(33/126 Pages) ICST

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Chapter 6 Functional Blocks

ICS1893CF, Rev. F, 03/01/07

Mar. 2007

ICS1893CF Data Sheet Rev. F - Release

6.4.2 100Base-TX Operation: MLT-3 Encoder/Decoder

When operating in the 100Base-TX mode, the ICS1893CF TP-PMD sublayer employs an MLT-3 encoder

and decoder. During data transmission, the TP-PMD encoder converts the NRZI bit stream received from

the PMA sublayer to a 3-level Multi-Level Transition code. The three levels are -1, 0, and +1. The results of

MLT-3 encoding provide a reduction in the transmitted energy over the critical frequency range from 20

MHz to 100 MHz. The TP-PMD MLT-3 decoder converts the received three-level signal back to an NRZI bit

stream.

6.4.3 100Base-TX Operation: DC Restoration

The ICS1893CF’s 100Base-TX operations uses a stream-cipher scrambler to minimize peak amplitudes in

the frequency spectrum. However, the nature of the stream cipher and MLT-3 encoding is such that long

sequences of consecutive zeros or ones can exist. These unbalanced data patterns produce an

undesirable DC component in the data stream known as ‘baseline wander’.

Baseline wander adversely affects the noise immunity of the receiver, because the ‘baseline’ signal moves

or ‘wanders’ from its nominal DC value. The ICS1893CF uses a unique technique to restore the DC

component ‘lost’ by the medium. As a result, the design is very robust, immune to noise and independent

of the data stream.

6.4.4 100Base-TX Operation: Adaptive Equalizer

The ICS1893CF has a TP-PMD sublayer that uses 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.

The ICS1893CF has an adaptive equalizer that accurately compensates for these losses in shielded

twisted-pair (STP) and unshielded twisted-pair (UTP) cables. The DSP-based adaptive equalizer uses a

technique that compensates for a wide range of cable lengths. The optimizing parameter for the

equalization process is the overall bit error rate of the ICS1893CF. This technique closes the loop on the

entire data reception process and provides a very high overall reliability.

6.4.5 100Base-TX Operation: Twisted-Pair Transmitter

The ICS1893CF uses the same Twisted-Pair Transmit pins (TP_TXP and TP_TXN) for both 10Base-T and

100Base-TX operations. Each 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 ICS1893CF interfaces with the medium through an isolation transformer (sometimes referred to as a

magnetic module). The ICS1893CF’s transmitter uses wave-shaping techniques to control the output

signal rise and fall times (thereby eliminating the need for external filters) and interfaces directly to the

isolation transformer.

Note:

1. In reference to the ICS1893CF, 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 6.5.11, “10Base-T Operation:

Twisted-Pair Transmitter”.

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