VT6103 datasheet(30/46 Pages) VIA

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VT6103 - Fast Ethernet 10 / 100 PHY / Transceiver

Revision 1.1 April 15, 2002

-24-

Functional Description

Technologies, Inc.

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Twisted Pair Receiver

Receiver - 100 Mbps

The TP receiver detects input signals from the twisted pair

input and converts them to a digital data bit stream ready for

clock and data recovery. The receiver can reliably detect data

from a 100Base-TX compliant transmitter that has been

passed through 0-100 meters of 100 Ohm category 5 UTP or

150 Ohm STP. The 100 Mbps receiver consists of a level

shifter, low pass filter, adaptive equalizer, peak detector,

comparator, baseline wander correction circuit, and MLT-3

decoder. A block diagram of the receiver is shown in Figure

The TP receiver inputs are assumed to be transformer

coupled and terminated by external resistors. The TP inputs

are then level shifted and pass through a 2nd order low pass

filter designed to eliminate any high frequency noise on the

input. The signal then goes to an adaptive equalizer. The

adaptive equalizer consists of a programmable bandpass filter

and peak detector. The adaptive equalizer uses the bandpass

filter

characteristic

compensate

for

the

low

pass

characteristics of the cable, and it uses the peak detector to

capture the peak value of the input waveform. It then uses the

peak value as a measure of cable length to adjust the pole and

zero placement of the bandpass filter. The bandpass filter is

digitally programmable and has a 5 bit digital input, called the

equalizer setting, that adjusts the frequency response to one of

32 settings. The peak detector captures the peak voltage of

the TP inputs, qualifies the input, and digitizes the qualified

value to a 5 bit digital result. This digital result, called the

equalizer setting, is used to adjust the programmable bandpass

filter characteristic. The peak detector qualifies the incoming

data stream by only allowing single and double baud wide

pulses to update the equalizer setting. If the digitized peak

value of any single or double baud wide pulse deviates from

the current equalizer setting in the same direction for more

than

consecutive

pulses,

the

equalizer

setting

incremented by one digital step only, independent of how

much the new setting and current setting differ. The equalizer

updating is only enabled when the receiver is in the unsquelch

state (valid data detected by the TP squelch circuit).

The

baseline wander correction circuit restores the DC component

of the input waveform that was removed by external

transformers by subtracting the filtered output of the data

comparator from the filtered output of the equalizer and

adding this difference back into the input of VT6103. The

baseline wander correction circuit is only enabled when the

descrambler is in the synchronized state. The comparators are

used to qualify and slice the data. There are two types of

receive comparators:

squelch and data.

The squelch

comparator compares the signal and the output of the LPF

before the equalizer against a fixed threshold. The output of

the squelch comparator is used by the squelch circuit and link

integrity blocks to qualify the data.

The data comparators

compare the signal at the output of the equalizer against fixed

positive and negative thresholds. The MLT-3 decoder takes

the three level MLT-3 encoded output data from the

comparators and converts it to normal NRZ data to be used for

clock and data recovery.

Receiver - 10 Mbps

The 10 Mbps receiver is able to detect input signals from the

twisted pair cable that are within the template shown in

IEEE802.3. The inputs are biased by internal resistors. The

TP inputs pass through a low pass filter designed to eliminate

any high frequency noise on the input.

The output of the

receive filter goes to two different types of comparators:

squelch and zero crossing.

The squelch comparator

determines whether the signal is valid and the zero crossing

comparator is used to sense the actual data transitions once the

signal is determined to be valid. The output of the squelch

comparator goes to the squelch circuit and is also used for link

pulse detection, SOI detection, and reverse polarity detection.

The output of the zero crossing comparator is used for clock

and data recovery in the Manchester decoder.

VT6103 Datasheet(PDF) 30 Page - VIA Technologies, Inc.

VT6103 Datasheet(HTML) 30 Page - VIA Technologies, Inc.

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