82503 datasheet(11/45 Pages) INTEL

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82503

290421 – 4

Figure 5 TPE Predistortion

33 Receive Blocks

331 MANCHESTER DECODER AND CLOCK

RECOVERY

The 82503 performs Manchester decoding and tim-

ing recovery of the incoming data in AUI and TPE

modes

The Manchester-encoded data stream is decoded to

separate the Receive Clock (RxC) and the Receive

Data (RxD) from the differential signal The 82503

uses an advanced digital technique to perform the

decoding function The use of digital circuitry instead

of analog circuitry (eg

a phase-lock loop) to per-

form the decoding ensures that the decoding func-

tion is less sensitive to variations in operating condi-

tions

A high-resolution phase reference is used to digitize

the phase of the incoming data bit-center transition

The digitizer has a phase resolution of 132 of a bit

time

The digitized phase is filtered by a digital low-pass

filter to remove rapid phase variations ie

phase

jitter Slow phase variations such as those caused

by small differences between the data frequency

and the clock frequency are not filtered by the low-

pass filter

The RxC generator digitally sets the phases of the

two RxC transitions to respectively lead and lag the

bit-center transition by

bit time RxC is used to

recover RxD by sampling the incoming data with an

edge-triggered flip-flop

Lock is achieved by reducing the time constant of

the digital filter to zero at the start of a new frame

Any uncertainty in the bit-center phase of the first

transition that is caused by jitter is subsequently re-

moved by gradually increasing the filter time con-

stant during the following preamble By that time the

phase of the bit center is output by the filter and

lock is achieved Lock is achieved within the first 14

bit times as seen by the AUI inputs The maximum

bit-cell timing distortion (jitter) tolerated by the Man-

chester decoder circuitry is g12 ns (preamble)

18 ns (data) for AUI and g135 ns for TPE (data

and preamble)

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